Surgical ablation probe for forming a circumferential lesion

ABSTRACT

This invention is a circumferential ablation device assembly and method which is adapted to form a circumferential conduction block in a pulmonary vein. The assembly generally comprises a handheld surgical ablation probe having a rigid shaft for insertion through a patient&#39;s chest and a circumferential ablation element mounted on the distal end portion of the shaft. The circumferential ablation element is adapted to ablate a circumferential region of tissue along a pulmonary vein wall which circumscribes the pulmonary vein lumen. The circumferential ablation element includes an expandable member for anchoring the distal end portion of the shaft in a body structure and an ultrasound transducer disposed within the expandable member for emitting ultrasonic energy to ablate the tissue in the pulmonary vein.

RELATED APPLICATIONS

[0001] The present application is a divisional of U.S. patentapplication Ser. No. 09/877,620 filed on Jun. 8, 2001, and claimspriority thereto under 35 U.S.C. §121. The present application alsoclaims priority under 35 U.S.C. §119(e) to U.S. Provisional ApplicationNo. 60/212879, filed Jun. 13, 2000.

TECHNICAL FIELD

[0002] The field of the invention relates to a surgical device andmethod. More particularly, it relates to a tissue ablation probe andmethod for ablating a circumferential region of tissue at a locationwhere a pulmonary vein extends from an atrium. The probe has particularutility during invasive or minimally invasive cardiac surgery.

BACKGROUND OF THE INVENTION

[0003] Many local energy delivery devices and methods have beendeveloped for the treatment of various abnormal tissue conditions in thebody, and particularly for treating abnormal tissue along body spacewalls which define various body spaces in the body. For example, variousdevices have been disclosed with the primary purpose of treating orrecanalizing atherosclerotic vessels with localized energy delivery.Several prior devices and methods combine energy delivery assemblies incombination with cardiovascular stent devices in order to locallydeliver energy to tissue in order to maintain patency in diseased lumenssuch as blood vessels. Endometriosis, another abnormal wall tissuecondition which is associated with the endometrial cavity and ischaracterized by dangerously proliferative uterine wall tissue along thesurface of the endometrial cavity, has also been treated by local energydelivery devices and methods.

[0004] Several other devices and methods have also been disclosed whichuse catheter-based heat sources for the intended purpose of inducingthrombosis and controlling hemorrhaging within certain body lumens suchas vessels. Detailed examples of local energy delivery devices andrelated procedures such as those of the types described above aredisclosed in the following references: U.S. Pat. No. 4,672,962 toHershenson; U.S. Pat. No. 4,676,258 to InoKuchi et al.; U.S. Pat. No.4,790,311 to Ruiz; 4,807,620 to Strut et al.; U.S. Pat. No. 4,998,933 toEggers et al.; U.S. Pat. No. 5,035,694 to Kasprzyk et al.; U.S. Pat. No.5,190,540 to Lee; U.S. Pat. No. 5,226,430 to Spears et al.; and U.S.Pat. No. 5,292,321 to Lee; U.S. Pat. No. 5,449,380 to Chin; U.S. Pat.No. 5,505,730 to Edwards; U.S. Pat. No. 5,558,672 to Edwards et al.; andU.S. Pat. No. 5,562,720 to Stem et al.; U.S. Pat. No. 4,449,528 to Authet al.; U.S. Pat. No. 4,522,205 to Taylor et al.; and U.S. Pat. No.4,662,368 to Hussein et al.; U.S. Pat. No. 5,078,736 to Behl; and U.S.Pat. No. 5,178,618 to Kandarpa.

[0005] Other prior devices and methods electrically couple fluid to anablation element during local energy delivery for treatment of abnormaltissues. Some such devices couple the fluid to the ablation element forthe primary purpose of controlling the temperature of the element duringthe energy delivery. Other such devices couple the fluid more directlyto the tissue-device interface either as another temperature controlmechanism or in certain other known applications as a carrier or mediumfor the localized energy delivery. Detailed examples of ablation deviceswhich use fluid to assist in electrically coupling electrodes to tissueare disclosed in the following references: U.S. Pat. No. 5,348,554 toImran et al.; U.S. Pat. No. 5,423,811 to Imran et al.; U.S. Pat. No.5,505,730 to Edwards; U.S. Pat. No. 5,545,161 to Imran et al.; U.S. Pat.No. 5,558,672 to Edwards et al.; U.S. Pat. No. 5,569,241 to Edwards;U.S. Pat. No. 5,575,788 to Baker et al.; U.S. Pat. No. 5,658,278 toImran et al.; U.S. Pat. No. 5,688,267 to Panescu et al.; U.S. Pat. No.5,697,927 to Imran et al.; U.S. Pat. No. 5,722,403 to McGee et al.; U.S.Pat. No. 5,769,846; and PCT Patent Application Publication No. WO97/32525 to Pomeranz et al.; and PCT Patent Application Publication No.WO 98/02201 to Pomeranz et al.

[0006] Other prior devices and methods have been disclosed which use aprobe as a surgical device, thereby allowing the physician to directlyapply an electrode to tissue. Detailed examples of surgical probes aredisclosed in the following references: U.S. Pat. No. 6,023,638 toSwanson; U.S. Pat. No. 4,841,979 to Dow et al.; U.S. Pat. No. 4,917,096to Englehart et al.; and U.S. Pat. No. 6,152,920 to Thompson et al.

Atrial Fibrillation

[0007] Cardiac arrhythmias, and atrial fibrillation in particular,persist as common and dangerous medical ailments associated withabnormal cardiac chamber wall tissue. In patients with cardiacarrhythmia, abnormal regions of cardiac tissue do not follow thesynchronous beating cycle associated with normally conductive tissue inpatients with sinus rhythm. Instead, the abnormal regions of cardiactissue aberrantly conduct electrical signals to adjacent tissue, therebydisrupting the cardiac cycle and causing an asynchronous cardiac rhythm.Such abnormal conduction is known to occur at various regions of theheart, such as, for example, in the region of the sino-atrial (SA) node,along the conduction pathways of the atrioventricular (AV) node and theBundle of His, or in the cardiac muscle tissue forming the walls of theventricular and atrial cardiac chambers.

[0008] Cardiac arrhythmias, including atrial arrhythmia, may be of amultiwavelet reentrant type, characterized by multiple asynchronousloops of electrical impulses that are scattered about the atrial chamberand are often self propagating. In the alternative or in addition to themultiwavelet reentrant type, cardiac arrhythmias may also have a focalorigin, such as when an isolated region of tissue in an atrium firesautonomously in a rapid, repetitive fashion. Cardiac arrhythmias,including atrial fibrillation, may be generally detected using theglobal technique of an electrocardiogram (EKG). More sensitiveprocedures of mapping the specific conduction along the cardiac chambershave also been disclosed, such as, for example, in U.S. Pat. No.4,641,649 to Walinsky et al. and in PCT Patent Application PublicationNo. WO 96/32897 to Desai.

[0009] A host of clinical conditions can result from the irregularcardiac function and resulting hemodynamic abnormalities associated withatrial fibrillation, including stroke, heart failure, and otherthromboembolic events. In fact, atrial fibrillation is believed to be asignificant cause of cerebral stroke, wherein the abnormal hemodynamicsin the left atrium caused by the fibrillatory wall motion precipitatethe formation of thrombus within the atrial chamber. A thromboembolismis ultimately dislodged into the left ventricle which thereafter pumpsthe embolism into the cerebral circulation where a stroke results.Accordingly, numerous procedures for treating atrial arrhythmias havebeen developed, including pharmacological, surgical, and catheterablation procedures.

[0010] Several pharmacological approaches intended to remedy orotherwise treat atrial arrhythmias have been disclosed, such as, forexample, those approaches disclosed in the following references: U.S.Pat. No. 4,673,563 to Berne et al.; U.S. Pat. No. 4,569,801 to Molloy etal.; and “Current Management of Arrhythmias” (1991) by Hindricks, et al.Such pharmacological solutions, however, are not generally believed tobe entirely effective in many cases, and are even believed in some casesto result in proarrhythmia and long term inefficacy.

[0011] Several surgical approaches have also been developed with theintention of treating atrial fibrillation. One particular example isknown as the “maze procedure,” as is disclosed by Cox, J. L. et al. in“The surgical treatment of atrial fibrillation. I. Summary” Thoracic andCardiovascular Surgery 101(3), pp. 402-405 (1991); and also by Cox, JLin “The surgical treatment of atrial fibrillation. IV. SurgicalTechnique”, Thoracic and Cardiovascular Surgery 101(4), pp. 584-592(1991). In general, the “maze” procedure is designed to relieve atrialarrhythmia by restoring effective atrial systole and sinus node controlthrough a prescribed pattern of incisions about the tissue wall. In theearly clinical experiences reported, the “maze” procedure includedsurgical incisions in both the right and the left atrial chambers.However, more recent reports predict that the surgical “maze” proceduremay be substantially efficacious when performed only in the left atrium.See Sueda et al., “Simple Left Atrial Procedure for Chronic AtrialFibrillation Associated With Mitral Valve Disease” (1996).

[0012] The “maze procedure” as performed in the left atrium generallyincludes forming vertical incisions from the two superior pulmonaryveins and terminating in the region of the mitral valve annulus,traversing the region of the inferior pulmonary veins en route. Anadditional horizontal line also connects the superior ends of the twovertical incisions. Thus, the atrial wall region bordered by thepulmonary vein ostia is isolated from the other atrial tissue. In thisprocess, the mechanical sectioning of atrial tissue eliminates thearrhythmogenic conduction from the boxed region of the pulmonary veinsto the rest of the atrium by creating conduction blocks within theaberrant electrical conduction pathways. Other variations ormodifications of this specific pattern just described have also beendisclosed, all sharing the primary purpose of isolating known orsuspected regions of arrhythmogenic origin or propagation along theatrial wall.

[0013] While the “maze” procedure and its variations as reported by Dr.Cox and others have met some success in treating patients with atrialarrhythmia, its highly invasive methodology is believed to beprohibitive in most cases. However, these procedures have provided aguiding principle that electrically isolating faulty cardiac tissue maysuccessfully prevent atrial arrhythmia, and particularly atrialfibrillation caused by arrhythmogenic conduction arising from the regionof the pulmonary veins.

[0014] Less invasive catheter-based approaches to treat atrialfibrillation have been disclosed which implement cardiac tissue ablationfor terminating arrhythmogenic conduction in the atria. Examples of suchcatheter-based devices and treatment methods have generally targetedatrial segmentation with ablation catheter devices and methods adaptedto form linear or curvilinear lesions in the wall tissue which definesthe atrial chambers. Some specifically disclosed approaches providespecific ablation elements which are linear over a defined lengthintended to engage the tissue for creating the linear lesion. Otherdisclosed approaches provide shaped or steerable guiding sheaths, orsheaths within sheaths, for the intended purpose of directing tipablation catheters toward the posterior left atrial wall such thatsequential ablations along the predetermined path of tissue may createthe desired lesion. In addition, various energy delivery modalities havebeen disclosed for forming atrial wall lesions, and include the use ofmicrowave, laser, ultrasound, thermal conduction, and more commonly,radio frequency energies to create conduction blocks along the cardiactissue wall.

[0015] Detailed examples of ablation device assemblies and methods forcreating lesions along an atrial wall are disclosed in the followingU.S. Pat. references: U.S. Pat. No. 4,898,591 to Jang et al.; U.S. Pat.No. 5,104,393 to Isner et al.; U.S. Pat. No. 5,427,119; U.S. Pat. No.5,487,385 to Avitall; U.S. Pat. No. 5,497,119 to Swartz et al.; U.S.Pat. No. 5,545,193 to Fleischman et al.; U.S. Pat. No. 5,549,661 toKordis et al.; U.S. Pat. No. 5,575,810 to Swanson et al.; U.S. Pat. No.5,564,440 to Swartz et al.; U.S. Pat. No. 5,592,609 to Swanson et al.;U.S. Pat. No. 5,575,766 to Swartz et al.; U.S. Pat. No. 5,582,609 toSwanson; U.S. Pat. No. 5,617,854 to Munsif; U.S. Pat. No. 5,687,723 toAvitall; U.S. Pat. No. 5,702,438 to Avitall. Other examples of suchablation devices and methods are disclosed in the following PCT PatentApplication Publication Nos.: WO 93/20767 to Stern et al.; WO 94/21165to Kordis et al.; WO 96/10961 to Fleischman et al.; WO 96/26675 to Kleinet al.; and WO 97/37607 to Schaer. Additional examples of such ablationdevices and methods are disclosed in the following published articles:“Physics and Engineering of Transcatheter Tissue Ablation”, Avitall etal., Journal of American College of Cardiology, Volume 22, No. 3:921-932(1993); and “Right and Left Atrial Radiofrequency Catheter Therapy ofParoxysmal Atrial Fibrillation,” Haissaguerre, et al., Journal ofCardiovascular Electrophysiology 7(12), pp. 1132-1144 (1996).

[0016] In addition to the known assemblies summarized above, additionaltissue ablation device assemblies have been recently developed for thespecific purpose of ensuring firm contact and consistent positioning ofa linear ablation element along a length of tissue. This is accomplishedby anchoring the element at least at one predetermined location alongthat length, such as in order to form a “maze”-type lesion pattern inthe left atrium. An example of such an assembly is disclosed in U.S.Pat. No. 5,971,983 to Lesh, issued Oct. 26, 1999, which is herebyincorporated by reference. The assembly includes an anchor at each oftwo ends of a linear ablation element in order to secure those ends toeach of two predetermined locations along a left atrial wall, such as attwo adjacent pulmonary veins, so that tissue may be ablated along thelength of tissue extending therebetween.

[0017] In addition to attempting atrial wall segmentation with longlinear lesions for treating atrial arrhythmia, other ablation devicesand methods have also been disclosed which are intended to useexpandable members such as balloons to ablate cardiac tissue. Some suchdevices have been disclosed primarily for use in ablating tissue wallregions along the cardiac chambers. Other devices and methods have beendisclosed for treating abnormal conduction of the left-sided accessorypathways, and in particular associated with “Wolff-Parkinson-White”syndrome—various such disclosures use a balloon for ablating from withina region of an associated coronary sinus adjacent to the desired cardiactissue to ablate. Further more detailed examples of devices and methodssuch as of the types just described are variously disclosed in thefollowing published references: Fram et al., in “Feasibility of RFPowered Thermal Balloon Ablation of Atrioventricular Bypass Tracts viathe Coronary Sinus: In vivo Canine Studies,” PACE, Vol. 18, p 1518-1530(1995); “Long-term effects of percutaneous laser balloon ablation fromthe canine coronary sinus”, Schuger C D et al., Circulation (1992)86:947-954; and “Percutaneous laser balloon coagulation of accessorypathways”, McMath L P et al., Diagn Ther Cardiovasc Interven 1991;1425:165-171.

Arrhythmias Originating from Foci in Pulmonary Veins

[0018] As briefly discussed above, various modes of atrial fibrillationhave been observed to be focal in nature, caused by the rapid andrepetitive firing of an isolated center within cardiac muscle tissueassociated with the atrium. Such foci may act as either a trigger ofatrial fibrillatory paroxysmal or may even sustain the fibrillation.Various disclosures have suggested that focal atrial arrhythmia oftenoriginates from at least one tissue region along one or more of thepulmonary veins of the left atrium, and even more particularly in thesuperior pulmonary veins.

[0019] Less invasive percutaneous catheter ablation techniques have beendisclosed which use end-electrode catheter designs with the intention ofablating and thereby treating focal arrhythmias in the pulmonary veins.These ablation procedures are typically characterized by the incrementalapplication of electrical energy to the tissue to form focal lesionsdesigned to terminate the arrhythmogenic conduction.

[0020] One example of a focal ablation method intended to treat focalarrhythmia originating from a pulmonary vein is disclosed byHaissaguerre, et al. in “Right and Left Atrial Radiofrequency CatheterTherapy of Paroxysmal Atrial Fibrillation” in Journal of CardiovascularElectrophysiology 7(12), pp. 1132-1144 (1996). Haissaguerre, et al.discloses radio frequency catheter ablation of drug-refractoryparoxysmal atrial fibrillation using linear atrial lesions complementedby focal ablation targeted at arrhythmogenic foci in a screened patientpopulation. The site of the arrhythmogenic foci were generally locatedjust inside the superior pulmonary vein, and the focal ablations weregenerally performed using a standard 4 mm tip single ablation electrode.

[0021] Another focal ablation method of treating atrial arrhythmias isdisclosed in Jais et al., “A focal source of atrial fibrillation treatedby discrete radio frequency ablation,” Circulation 95:572-576 (1997).Jais et al. discloses treating patients with paroxysmal arrhythmiasoriginating from a focal source by ablating that source. At the site ofarrhythmogenic tissue, in both right and left atria, several pulses of adiscrete source of radio frequency energy were applied in order toeliminate the fibrillatory process.

[0022] Other assemblies and methods have been disclosed addressing focalsources of arrhythmia in pulmonary veins by ablating circumferentialregions of tissue either along the pulmonary vein, at the ostium of thevein along the atrial wall, or encircling the ostium and along theatrial wall. More detailed examples of device assemblies and methods fortreating focal arrhythmia as just described are disclosed in PCT PatentApplication Publication No. WO 99/02096 to Diederich et al., and also inthe following Patents and pending U.S. Pat. application Ser. Nos.08/889,798 for “Circumferential Ablation Device Assembly” to Lesh etal., filed Jul. 8, 1997, now U.S. Pat. No. 6,024,740, issued on Feb. 15,2000; Ser. No. 08/889,835 for “Device and Method for Forming aCircumferential Conduction Block in a Pulmonary Vein” to Lesh, filedJul. 8, 1997, now U.S. Pat. No. 6,012,457, issued Jan. 11, 2000; Ser.No. 09/199,736 for “Circumferential Ablation Device Assembly” toDiederich et al., filed Feb. 3, 1998, now U.S. Pat. No. 6,117,101,issued Sep. 12, 2000; and Ser. No. 09/260,316 for “Tissue AblationDevice Assembly and Method of Forming a Conduction Block Along a Lengthof Tissue” to Langberg et al., filed Mar. 1, 1999.

[0023] Another specific device assembly and method which is intended totreat focal atrial fibrillation by ablating a circumferential region oftissue between two seals in order to form a conduction block to isolatean arrhythmogenic focus within a pulmonary vein is disclosed in U.S.Pat. No. 5,938,660 and a related PCT Patent Application Publication No.WO 99/00064. The disclosures of these references are herein incorporatedin their entirety by reference thereto.

[0024] The device assemblies and methods disclosed heretofore forablating a circumferential region of tissue generally involvecatheter-based therapies wherein an ablation element is mounted on thedistal end of the catheter for placement in a pulmonary vein, such as ina percutaneous translumenal procedure. However, in certain surgicalapproaches, such as trans-thoracic surgery, a physician can access thepulmonary vein in a more direct manner, such as through an atriotomy,thereby obviating the need for a catheter-based device. None of thedisclosed circumferential ablation devices provides a device assembly ormethod that can be used to directly place an ablation element in apulmonary vein during trans-thoracic or minimally invasive cardiacsurgical procedures.

[0025] Thus, a need exists for a rigid, handheld surgical probe fordelivering ablative energy at a location where a pulmonary vein extendsfrom an atrial wall. It is desirable that such a surgical probe beadapted to precisely deliver ablative energy to form a circumferentiallesion to treat atrial fibrillation.

SUMMARY OF THE INVENTION

[0026] The preferred embodiments of the present invention provide aergonomically designed, handheld surgical ablation probe that issubstantially rigid and can be used to directly apply ablative energy toform a circumferential lesion in a pulmonary vein during trans-thoracicor minimally invasive surgery. The preferred embodiments are providedwith a deflectable tip for enhanced maneuverability and preciseplacement of the ablation element in a pulmonary vein. The preferredembodiments also include an expandable member on the distal end foranchoring the ablation element to the surrounding tissue duringablation. The surgical ablation probe is adapted for use with varioustypes of ablation elements, such as, for example, an ultrasonictransducer.

[0027] One aspect of the present invention involves a medical devicesystem for ablating a circumferential region of tissue in order to forma circumferential conduction block at a location where a pulmonary veinextends from an atrium in a patient's heart. Such conduction block maybe formed in order to, for example: electrically isolate a focal sourceof arrhythmia in the pulmonary vein from the rest of the atrium; orconnect linear lesions such that a pattern of conduction blocks may beformed to isolate a posterior region of the atrial wall from the rest ofthe atrium.

[0028] In one mode, a tissue ablation probe of the present medicaldevice system ablates a substantial portion of a circumferential regionof tissue at a location in a patient's body where a pulmonary veinextends from an atrium in a patient. The ablation probe includes ahandle attached to a proximal end portion of a relatively short shaft(i.e., short as compared to a percutaneous translumenal catheter). Anablation member is coupled to a distal end portion of the shaft. Theablation member also comprises an expandable member coupled to thedistal end portion of the shaft, wherein the expandable member isadjustable from a collapsed position to an expanded position. Theexpandable member is adapted to engage a substantial portion of thecircumferential region of tissue when in the expanded position. Theablation member also has an ablation element that is adapted to ablateat least a portion of the substantial portion of the circumferentialregion of tissue.

[0029] The ablation element employed in differing modes of the tissueablation probe can comprise a microwave ablation element, a cryogenicablation element, a thermal ablation element, a light-emitting ablationelement (e.g., laser), an ultrasound transducer, or an electricalablation element, such as an RF ablation element.

[0030] In one mode of the ablation apparatus, the expandable member isan inflatable balloon. The expandable member can have an outer surfacethat is adapted to contact the substantial portion of thecircumferential region of tissue along an ablative path when theexpandable member is adjusted to the expanded position.

[0031] The ablation member may also include a sensor that is coupled tothe expandable member at a location at least when the expandable memberis in the expanded position. A conductor is coupled to the sensor in amanner that does not substantially affect the adjustment of theexpandable member from the collapsed positioned to an expanded position.In a preferred form, the conductor also is coupled to a coupler at theproximal end portion of the handle.

[0032] In a preferred mode, the ablation element preferably comprises anultrasound transducer adapted to emit a circumferential path ofultrasound ablative energy. The sensor may be positionable within thecircumferential path when the expandable member is in the expandedposition.

[0033] In accordance with one method of using the ablation probe of thepresent invention, during a trans-thoracic (open heart) or minimallyinvasive cardiac procedure, e.g., for mitral valve replacement, aphysician can place the distal end of the shaft, including the ablationmember, at a location where a pulmonary vein extends from an atrium. Theexpandable member is expanded to secure and/or ablatively couple theablation member to the location and the ablation element is energized toablate at least a substantial portion of the circumferential region oftissue.

[0034] Also disclosed is a method for monitoring the ablation of asubstantial portion of a circumferential region of tissue at a locationwhere a pulmonary vein extends from an atrium. The method involvespositioning an ablation member, which has an ablation element, along thelocation where the pulmonary vein extends from the atrium. The ablationelement is activated to ablate the substantial portion of thecircumferential region of tissue. This can be done simultaneously orthrough a sequential series of ablation steps (temporal and/or spatial).Temperature is monitored along the substantial portion of thecircumferential region of tissue. The ablation element is deactivatedwhen the temperature along the substantial portion of thecircumferential region of tissue has reached either a firstpredetermined value or a second predetermined valve for a predeterminedperiod of time.

[0035] While various aspects and features of the present invention haveparticular utility in the context of tissue ablation apparatuses andablation processes, such aspects and features also can be practicedapart from such devices and methods.

[0036] Various aspects, features and advantages of the presentinvention, in addition to those described above, will also becomeapparent from the following description of preferred modes of theinvention and from the appended description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The advantages and features of the disclosed invention willreadily be appreciated by persons skilled in the art from the followingdetailed description when read in conjunction with the drawings listedbelow.

[0038]FIG. 1 shows schematic, perspective views of various exemplarycircumferential conduction blocks formed in pulmonary vein wall tissuewith a circumferential ablation device assembly.

[0039]FIG. 2 diagrammatically shows the sequential, general steps fortreating atrial arrhythmia.

[0040]FIG. 3 diagrammatically shows the steps of forming a conductionblock at a location where a pulmonary vein extends from an atrium.

[0041]FIG. 4 shows a perspective view of a circumferential ablationprobe during use in a left atrium subsequent to performing atrial accesssteps according to the method of FIG. 3.

[0042]FIG. 5 shows a similar perspective view of the circumferentialablation device assembly shown in FIG. 4, and further shows thecircumferential ablation probe with an expandable member shown in aradially expanded condition during use in ablating a circumferentialregion of tissue along a pulmonary vein wall.

[0043]FIG. 6 shows a similar perspective view of the left atrium that isshown in FIGS. 4-5, although illustrating a cross-sectional view of acircumferential lesion after being formed by the circumferential probeablation according to the method of FIG. 3.

[0044]FIG. 7 shows a perspective view of another circumferentialablation probe variation during use in a left atrium according to themethod of FIG. 3 wherein the ablation element is formed to also engage acircumferential path of tissue along the left posterior wall whichsurrounds the pulmonary vein ostium.

[0045]FIG. 8 shows a perspective view of the circumferential ablationprobe of the FIG. 7 variation during use in a left atrium according tothe method of FIG. 3, showing the expandable member after advancing itinto and engaging a pulmonary vein ostium while in the radially expandedposition.

[0046] FIGS. 9 shows the same perspective view of the left atrium shownin FIGS. 7-8, although shown after forming a circumferential conductionblock according to the circumferential ablation procedure of FIG. 3wherein the circumferential lesion extends onto the left posterior wall.

[0047] FIGS. 10 shows a perspective view of another circumferentialablation probe during use in a left atrium wherein the ablation elementis formed to engage only a circumferential path of tissue along the leftposterior wall and does not extend into the pulmonary vein.

[0048]FIG. 11 shows a resulting circumferential conduction block orlesion which may be formed with the assembly and the method of use shownin FIG. 10.

[0049]FIG. 12 diagrammatically shows a method for using acircumferential ablation device assembly to form a circumferentialconduction block in a pulmonary vein in combination with a method forforming long linear lesions between pulmonary vein ostia in aless-invasive “maze”-type procedure.

[0050]FIG. 13 shows a perspective view of a segmented left atrium afterforming several long linear lesions between adjacent pairs of pulmonaryvein ostia according to the method of FIG. 12.

[0051]FIG. 14 shows a similar perspective view as that shown in FIG. 13,although showing a circumferential ablation device assembly during usein forming a circumferential lesion in a pulmonary vein which intersectswith two linear lesions that extend into the pulmonary vein, accordingto the method of FIG. 12.

[0052]FIG. 15 shows a perspective view of a segmented left posterioratrial wall with a lesion pattern which results from combining theformation of two linear lesions according to FIG. 12 with the formationof a circumferential conduction block according to the methods anddevices shown in FIGS. 7-8.

[0053]FIG. 16 shows a perspective view of a segmented left posterioratrial wall with a lesion pattern which results from combining theformation of two linear lesions according to FIG. 12 with the formationof a circumferential conduction block according to the methods anddevices shown in FIGS. 10-11.

[0054]FIG. 17 shows a schematic perspective view of a left posterioratrial wall with one complete lesion pattern in a variation of aless-invasive “maze”-type procedure wherein circumferential conductionblocks are formed along circumferential paths of tissue along a leftposterior atrial wall such that each circumferential conduction blocksurrounds a pulmonary vein ostium, each pair of vertically adjacentcircumferential conduction blocks intersects, and each pair ofhorizontally adjacent circumferential conduction blocks are connectedwith one of two linear lesions extending between the respective pair ofhorizontally adjacent pulmonary vein ostia.

[0055]FIG. 18 diagrammatically shows a further method for using thecircumferential ablation device assembly of the present invention toform a circumferential conduction block in a pulmonary vein wall,wherein signal monitoring and “post-ablation” test elements are used tolocate an arrhythmogenic origin along the pulmonary vein wall and totest the efficacy of a circumferential conduction block in the wall,respectively.

[0056]FIG. 19 shows a circumferential ablation probe in accordance witha preferred mode of the present invention having an inflatable balloonand an ultrasonic transducer disposed on the distal end for forming acircumferential lesion to treat atrial fibrillation.

[0057]FIG. 20 shows the circumferential ablation probe of FIG. 19wherein the inflatable balloon is in a collapsed state.

[0058]FIG. 21 shows the distal end portion of the circumferentialablation probe of FIG. 19 wherein the inflatable balloon is in aninflated state.

[0059]FIG. 22 is a cross-sectional view taken along line 22-22 of thecircumferential ablation probe shown in FIG. 20.

[0060]FIG. 23 is a cross-sectional view taken along line 23-23 of thecircumferential ablation probe shown in FIG. 20.

[0061]FIG. 24 is a perspective view of a circumferential ablation probehaving a deflectable tip portion whereby the distal end is shown invarious deflected positions.

[0062]FIG. 25 is a schematic view of the proximal end of acircumferential ablation probe of FIG. 19, showing proximal extensionsof the various lumens in the multilumen probe shaft.

[0063] FIGS. 26A-B show perspective views of another circumferentialablation member variation for use in a circumferential ablation deviceassembly for pulmonary vein isolation, showing a circumferentialablation electrode circumscribing the working length of an expandablemember with a secondary shape along the longitudinal axis of the workinglength which is a modified step shape, the expandable member being shownin a radially collapsed position and also in a radially expandedposition, respectively.

[0064] FIGS. 26C-D show perspective views of two circumferentialablation electrodes which form equatorial or otherwise circumferentiallyplaced bands that circumscribe the working length of an expandablemember and that have serpentine and sawtooth secondary shapes,respectively, relative to the longitudinal axis of the expandable memberwhen adjusted to a radially expanded position.

[0065] FIGS. 26E-F show perspective views of another circumferentialablation element which includes a plurality of individual ablationelectrodes that are spaced circumferentially to form an equatorial bandwhich circumscribes the working length of an expandable member either inan equatorial location or an otherwise circumferential location that isbounded both proximally and distally by the working length, and whichare adapted to form a continuous circumferential lesion while theworking length is adjusted to a radially expanded position.

[0066]FIG. 27A shows a cross-sectional view of another circumferentialablation member for use in a circumferential ablation device assemblyfor pulmonary vein isolation, wherein the circumferential ablationelement circumscribes an outer surface of an expandable membersubstantially along its working length and is insulated at both theproximal and the distal ends of the working length to thereby form anuninsulated equatorial band in a middle region of the working length orotherwise circumferential region of the working length which is boundedboth proximally and distally by end portions of the working length,wherein the member is adapted to ablate a circumferential path of tissueengaged by the equatorial band.

[0067]FIG. 27B shows a perspective view of another circumferentialablation member which is adapted for use in a circumferential ablationdevice assembly for pulmonary vein isolation, wherein the expandablemember is shown to be a cage of coordinating wires which are adapted tobe adjusted from a radially collapsed position to a radially expandedposition in order to engage electrode elements on the wires about acircumferential pattern of tissue to be ablated.

[0068]FIG. 28 shows a cross-sectional view of another circumferentialablation element which is adapted for use in a circumferential ablationdevice assembly for pulmonary vein isolation. A superelastic, loopedelectrode element is shown at the distal end of a pusher and is adaptedto circumferentially engage pulmonary vein wall tissue to form acircumferential lesion as a conduction block that circumscribes thepulmonary vein lumen.

[0069]FIG. 29A shows a longitudinal cross-sectional view of anothercircumferential ablation probe, and shows the ablation element toinclude a single cylindrical ultrasound transducer which is positionedalong an inner member within an expandable balloon which is furthershown in a radially expanded condition.

[0070]FIG. 29B shows a transverse cross-sectional view of thecircumferential ablation probe shown in FIG. 29A taken along line29B-29B.

[0071]FIG. 29C shows a transverse cross-sectional view of thecircumferential ablation probe shown in FIG. 29A taken along line29C-29C.

[0072]FIG. 29D shows a perspective view of the ultrasonic transducer ofFIG. 29A in isolation.

[0073]FIG. 29E shows a modified version of the ultrasonic transducer ofFIG. 29D with individually driven sectors.

[0074]FIG. 30A shows a perspective view of a circumferential ablationprobe similar to the probe shown in FIG. 29A, and shows the distal endportion of the circumferential ablation probe during one mode of use informing a circumferential conduction block in a pulmonary vein in theregion of its ostium along a left atrial wall (shown in cross-section inshadow).

[0075]FIG. 30B shows a similar perspective and cross-sectional shadowview of a circumferential ablation probe and pulmonary vein ostium asthat shown in FIG. 30A wherein the inflatable balloon has a taperedouter diameter for conforming to the shape of the ostium.

[0076]FIG. 30C shows a similar view to that shown in FIGS. 30A-B,although showing another circumferential ablation probe wherein theballoon has a “pear”-shaped outer diameter with a contoured surfacealong a taper which is adapted to seat in the ostium of a pulmonaryvein.

[0077]FIG. 30D shows a cross-sectional view of one circumferentialconduction block which may be formed by use of a circumferentialablation probe such as that shown in FIG. 30C.

[0078]FIG. 31A shows a cross-sectional view of the distal end portion ofanother circumferential ablation probe, wherein an outer shield orfilter is provided along the balloon's outer surface in order to form apredetermined shape for the circumferential ablation element created bysonic transmissions from the inner ultrasound transducer.

[0079]FIG. 31B shows a similar view as that shown in FIG. 31A, althoughshowing the distal end portion of another circumferential ablation probewhich includes a heat sink as an equatorial band within thecircumferential path of energy emission from an inner ultrasoundtransducer.

[0080]FIG. 32A is a perspective view of a suspended coaxial ultrasoundtransducer wherein an outer layer is used to suspend the transducer overthe probe such that a radial separation is maintained therebetween.

[0081]FIG. 32B is a cross-sectional view taken along line 32B-32Bthrough the transducer of FIG. 32A.

[0082] Further aspects, features and advantages of this invention willbecome apparent from the detailed description of the modes of theinvention which follows.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0083] As will be described with reference to the detailed embodimentsbelow, the invention is well adapted to treat patients with atrialarrhythmia by ablating a circumferential region of tissue at a locationwhere a pulmonary vein extends from an atrium, such as (a) where cardiactissue extends up from the vein; or (b) along the vein's ostium alongthe atrial wall; or (c) along the atrial wall and surrounding the vein'sostium. By ablating such a circumferential region of tissue, acircumferential conduction block is formed which either isolates theatrium from an arrhythmogenic focus upstream of the conduction blockrelative to the vein, or ablates the focus.

[0084] For the purpose of further illustration, particular embodimentsfor pulmonary vein isolation are shown and described by reference toFIGS. 1-18, with the related method of treatment broadly illustrateddiagrammatically in the flow diagram of FIG. 2. The details of thecircumferential ablation probe of the present invention are described byreference to FIGS. 19-32B.

Definition of Terms

[0085] The following terms will have the following meanings throughoutthis specification.

[0086] The terms “body space,” including derivatives thereof, is hereinintended to mean any cavity or lumen within the body which is defined atleast in part by a tissue wall. For example, the cardiac chambers, theuterus, the regions of the gastrointestinal tract, and the arterial orvenous vessels are all considered illustrative examples of body spaceswithin the intended meaning.

[0087] The term “body lumen,” including derivatives thereof, is hereinintended to mean any body space which is circumscribed along a length bya tubular tissue wall and which terminates at each of two ends in atleast one opening that communicates externally of the body space. Forexample, the large and small intestines, the vas deferens, the trachea,and the fallopian tubes are all illustrative examples of lumens withinthe intended meaning. Blood vessels are also herein considered lumens,including regions of the vascular tree between their branch points. Moreparticularly, the pulmonary veins are lumens within-the intendedmeaning, including the region of the pulmonary veins between thebranched portions of their ostia along a left ventricle wall, althoughthe wall tissue defining the ostia typically presents uniquely taperedlumenal shapes.

[0088] The terms “circumference” or “circumferential”, includingderivatives thereof, as used herein include a continuous path or linewhich forms an outer border or perimeter that surrounds and therebydefines an enclosed region of space. Such a continuous path starts atone location along the outer border or perimeter, and translates alongthe outer border or perimeter until it is completed at the originalstarting location to enclose the defined region of space. The relatedterm “circumscribe,” including derivatives thereof, as used hereinincludes a surface to enclose, surround, or encompass a defined regionof space. Therefore, a continuous line which is traced around a regionof space and which starts and ends at substantially the same location“circumscribes” the region of space and has a “circumference” whichincludes the distance the line travels as it translates along the pathcircumscribing the space.

[0089] Still further, a circumferential path or element may include oneor more of several shapes, and may be for example circular, oblong,ovular, elliptical, or otherwise planar enclosures. A circumferentialpath may also be three dimensional, such as for example twoopposite-facing semi-circular paths in two different parallel oroff-axis planes that are connected at their ends by line segmentsbridging between the planes.

[0090] A “circumferential conduction block” according to the presentinvention is formed along a region of tissue that follows acircumferential path along the pulmonary vein wall, circumscribing thepulmonary vein lumen and transecting the pulmonary vein relative toelectrical conduction along its longitudinal axis. The transectingcircumferential conduction block therefore isolates electricalconduction between opposite longitudinal portions of the pulmonary wallrelative to the conduction block and along the longitudinal axis.

[0091] For purpose of further illustration, FIGS. 1A-D therefore showvarious circumferential paths A, B, C, and D, respectively, eachtranslating along a portion of a pulmonary vein wall and circumscribinga defined region of space, shown at a, b, c, and d also respectively,each circumscribed region of space being a portion of a pulmonary veinlumen. For still further illustration-of the three-dimensionalcircumferential case shown in FIG. 1D, FIG. 1E shows an explodedperspective view of circumferential path D as it circumscribesmultiplanar portions of the pulmonary vein lumen shown at d′, d″, andd′″, which together make up region d as shown in FIG. 1D.

[0092] The term “transect”, including derivatives thereof, is alsoherein intended to mean to divide or separate a region of space intoisolated regions. Thus, each of the regions circumscribed by thecircumferential paths shown in FIGS. 1A-D transects the respectivepulmonary vein, including its lumen and its wall, to the extent that therespective pulmonary vein is divided into a first longitudinal regionlocated on one side of the transecting region, shown, for example, atregion “X” in FIG. 1A, and a second longitudinal region on the otherside of the transecting plane, shown, for example, at region “Y” also inFIG. 1A.

[0093] The terms “ablate” or “ablation,” including derivatives thereof,are hereafter intended to include the substantial altering of themechanical, electrical, chemical, or other structural nature of tissue.In the context of ablation applications shown and described withreference to the variations of the illustrative device below, “ablation”is intended to include sufficient altering of tissue properties tosubstantially block conduction of electrical signals from or through theablated cardiac tissue.

[0094] The term “element” within the context of “ablation element” isherein intended to include a discrete element, such as an electrode, ora plurality of discrete elements, such as a plurality of spacedelectrodes, which are positioned so as to collectively ablate a regionof tissue.

[0095] Therefore, an “ablation element” according to the defined termscan include a variety of specific structures adapted to ablate a definedregion of tissue. For example, one suitable ablation element for use inthe present invention may be formed, according to the teachings of theembodiments below, from an “energy emitting” type of structure which isadapted to emit energy sufficient to ablate tissue when coupled to andenergized by an energy source. Suitable “energy emitting” ablationelements for use in the present invention may therefore include, forexample: an electrode element adapted to couple to a direct current(“DC”) or alternating current (“AC”) current source, such as a RadioFrequency (“RF”) current source; an antenna element which is energizedby a microwave energy source; a heating element, such as a metallicelement or other thermal conductor which is energized to emit heat suchas by convective or conductive heat transfer, by resistive heating dueto current flow, or by optical heating with light; a light emittingelement, such as a fiber optic element which transmits light sufficientto ablate tissue when coupled to a light source; or an ultrasonicelement such as an ultrasound crystal element which is adapted to emitultrasonic sound waves sufficient to ablate tissue when coupled to asuitable excitation source.

[0096] In addition, other elements for altering the nature of tissue maybe suitable as “ablation elements” under the present invention whenadapted according to the detailed description of the invention below.For example, a cryogenic ablation (cryoblation) element adapted tosufficiently cool tissue to substantially alter the structure thereofmay be suitable if adapted according to the teachings of the currentinvention. Furthermore, a fluid delivery element, such as a discreteport or a plurality of ports which are fluidly coupled to a fluiddelivery source, may be adapted to infuse an ablating fluid, such as afluid containing alcohol, into the tissue adjacent to the port or portsto substantially alter the nature of that issue.

Formation of a Circumferential Conduction Block

[0097] In the context of the illustrative application of use,catheter-based cardiac arrhythmia therapies generally involveintroducing an ablation catheter into a cardiac chamber, such as in apercutaneous translumenal procedure, wherein an ablation element on thecatheter's distal end portion is positioned at or adjacent to theaberrant conductive tissue. The ablation element is used to ablate thetargeted tissue thereby creating a lesion. A further description of suchprocedure is described in U.S. Pat. No. 6,024,740, issued Feb. 15, 2000,which is hereby incorporated by reference. The present invention isaimed at an ablation device with many of the same characteristics of ourpreviously patented catheter-based systems, however, the presentinvention is designed for direct placement at the location of pulmonaryvein terminus during open heart or minimally invasive cardiac surgicalprocedures.

[0098] Returning to the inventive method as shown in FIG. 2, a patientdiagnosed with atrial arrhythmia according to diagnosing step (1) istreated with a circumferential conduction block according to treatmentstep (2). In one aspect, a patient diagnosed according to diagnosis step(1) with multiple wavelet arrhythmia originating from multiple regionsalong the atrial wall may also be treated in part by forming thecircumferential conduction block according to treatment step (2),although as an adjunct to forming long linear regions of conductionblock between adjacent pulmonary vein ostia in a less-invasive“maze”-type catheter ablation procedure. More detail regarding thisparticular aspect of the inventive method is provided below withreference to FIGS. 12-17.

[0099] In another aspect of the method of FIG. 2, a patient diagnosedwith focal arrhythmia originating from an arrhythmogenic origin or focusin a pulmonary vein is treated according to this method when thecircumferential conduction block is formed along a circumferential pathof wall tissue that either includes the arrhythmogenic origin or isbetween the origin and the left atrium. In the former case, thearrhythmogenic tissue at the origin is destroyed by the conduction blockas it is formed through that focus. In the latter case, thearrhythmogenic focus may still conduct abnormally, although suchaberrant conduction is prevented from entering and affecting the atrialwall tissue due to the intervening circumferential conduction block.

[0100] In still a further aspect of the method shown in FIG. 2, thecircumferential conduction block may be formed in one of several waysaccording to treatment step (2). In one example not shown, thecircumferential conduction block may be formed by a surgical incision orother method to mechanically transect the pulmonary vein, followed bysuturing the transected vein back together. As the circumferentialinjury is naturally repaired, such as through a physiologic scarringresponse common to the “maze” procedure, electrical conduction willgenerally not be restored across the injury site. In another example notshown, a circumferential conduction block of one or more pulmonary veinsmay be performed in an epicardial ablation procedure, wherein anablation element is either placed around the target pulmonary vein or istranslated circumferentially around it while being energized to ablatethe adjacent tissue in an “outside-in” approach. This alternative methodmay be performed during an open chest-type procedure, or may be doneusing other known epicardial access techniques.

[0101]FIG. 3 diagrammatically shows the sequential steps of a method forusing a circumferential ablation probe assembly to form acircumferential conduction block in a pulmonary vein. Thecircumferential ablation method according to FIG. 3 includes:positioning a circumferential ablation element at an ablation regionalong the pulmonary vein according to a series of detailed steps showncollectively in FIG. 3 as positioning step (3); and thereafter ablatinga continuous circumferential region of tissue in the pulmonary vein wallat the ablation region according to ablation step (4). Subsequent togaining pulmonary vein access, positioning step (3) of FIG. 3 nextincludes positioning a circumferential ablation element at an ablationregion of the pulmonary vein where the circumferential conduction blockis to be desirably formed.

[0102]FIG. 4 shows a circumferential ablation probe 100 during use inperforming positioning step (3) just described with reference to FIG. 3.The circumferential ablation probe 100 generally comprises a shaft 102,an atraumatic tip 110, and a circumferential ablation member 104. Thecircumferential ablation member 104 includes an expandable member 106and an ablation element 108. The ablation element 108 includes acircumferential band (shown in hatched) on the outer surface of theexpandable member that ablatively couples to the surrounding tissue toform a circumferential lesion.

[0103] More specifically, FIG. 4 shows the circumferential ablationprobe 100 subsequent to advancing the distal end portion into the inneratrium according to step (3) of FIG. 3, and also subsequent toadvancement and positioning of the circumferential ablation member 104within a pulmonary vein, also according to step (3) of FIG. 3. FIG. 4also schematically illustrates the proximal end of the circumferentialablation probe 100 including an expansion actuator 154, an ablationactuator 156, and a ground patch 195.

[0104]FIG. 4 shows the circumferential ablation probe 100 with theexpandable member 106 in a radially collapsed position adapted fordelivery into the pulmonary vein according to positioning step (3) ofFIG. 3. However, the expandable member 106 is adjustable to a radiallyexpanded position when actuated by the expansion actuator 154, as shownin FIG. 5. The expansion actuator 154 may include, but is not limitedto, a pressurizable fluid source. According to the expanded state shownin FIG. 5, the expandable member 106 includes a working length Lrelative to the longitudinal axis of the elongate catheter body whichhas a larger expanded outer diameter OD than when in the radiallycollapsed position. Furthermore, the expanded outer diameter OD issufficient to circumferentially engage the ablation region of thepulmonary vein. Therefore, the terms “working length” are hereinintended to mean the length of an expandable member which, when in aradially expanded position, has an expanded outer diameter that is: (a)greater than the outer diameter of the expandable member when in aradially collapsed position; and (b) sufficient to engage a body spacewall or adjacent ablation region surrounding the expandable member, atleast on two opposing internal sides of the body space wall or adjacentablation region, with sufficient surface area to anchor the expandablemember.

[0105] The circumferential ablation element 108 includes acircumferential band on the outer surface of the expandable member 106which is coupled to an ablation actuator 156 at a proximal end portionof the probe shaft (shown schematically in FIG. 4). The ablation element108 is actuated by ablation actuator 156 to ablatively couple to thesurrounding circumferential path of tissue in the pulmonary vein wall,thereby forming a circumferential lesion that circumscribes thepulmonary vein lumen and transects the electrical conductivity of thepulmonary vein to block conduction in a direction along its longitudinalaxis.

[0106]FIG. 6 shows pulmonary vein 52 after removing the circumferentialablation device assembly subsequent to forming a circumferential lesion44 around the ablation region of the pulmonary vein wall 48 according tothe use of the circumferential ablation probe assembly 100 shown instepwise fashion in FIGS. 3-5. The circumferential lesion 44 is shownlocated along the pulmonary vein adjacent to the pulmonary vein ostium54, and is shown to also be “transmural,” which is herein intended tomean extending completely through the wall, from one side to the other.Also, the circumferential lesion 44 is shown in FIG. 6 as a “continuous”lesion, which is herein intended to mean without gaps around thepulmonary vein wall circumference, thereby circumscribing the pulmonaryvein lumen.

[0107] However, it is believed that a circumferential ablation probewith a circumferential ablation element may leave some tissue, eithertransmurally or along the circumference of the lesion, which is notactually ablated, but which is not substantial enough to allow for thepassage of conductive signals. Therefore, the terms “transmural” and“continuous” as just defined are intended to have functionallimitations, wherein some tissue in the ablation region may be unablatedbut there are no fuinctional gaps which allow for symptomaticallyarrhythmogenic signals to conduct through the conduction block and intothe atrium from the pulmonary vein.

[0108] Moreover, it is believed that the functionally transmural andcontinuous lesion qualities just described are characteristic of acompleted circumferential conduction block in the pulmonary vein. Such acircumferential conduction block thereby transects the vein, isolatingconduction between the portion of the vein on one longitudinal side ofthe lesion and the portion on the other side. Therefore, any foci oforiginating arrhythmogenic conduction which is opposite the conductionblock from the atrium is prevented by the conduction block fromconducting down into the atrium and atrial arrhythmic affects aretherefore nullified.

[0109] FIGS. 7-8 illustrate another variation of a circumferentialablation member 204 that includes a radially compliant expandable member206 and an ablation element 208 adapted to ablatively couple to a largerregion of tissue. FIG. 7 illustrates the expandable member 206 afterbeing adjusted to a radially expanded position while located in the leftatrium. FIG. 8 further shows the expandable member 206 after beingadvanced into the pulmonary vein 52 until at least a portion of theexpanded working length L of the ablation element 208, which includes acircumferential band, engages the pulmonary vein ostium (shown as 54 inFIG. 7). FIG. 9 illustrates a portion of the circumferential lesion 44′that provides a circumferential conduction block in the region of thepulmonary vein ostium 54 subsequent to actuating the circumferentialablation element.

[0110] In the embodiment described in FIGS. 7-8, the expandable member206 is formed to also engage a circumferential path of tissue along theleft posterior atrial wall that surrounds the ostium 54. Moreover, theablation element 208 of the circumferential ablation member 204 is alsothereby adapted to engage that atrial wall tissue. Therefore, thecircumferential lesion 44′ formed according to the method shown in partin FIG. 9, and just described in sequential steps by reference to FIGS.7-8, includes ablating a circumferential path of atrial walltissue-which surrounds the ostium 54. Accordingly, the entire pulmonaryvein 52, including the ostium 54, is thereby electrically isolated fromat least a substantial portion of the left atrial wall. Thecircumferential lesion 44′ also isolates the other of the pulmonary veinostia, as would be apparent to one of ordinary skill according to thesequential method steps shown in FIGS. 7-8 and by further reference tothe resulting circumferential lesion 44′ shown in FIG. 9.

[0111]FIG. 10 shows yet another variation of a circumferential ablationmember 308 and use thereof for electrically isolating a pulmonary veinand ostium from a substantial portion of the left posterior atrial wall.However, unlike the embodiment previously shown and described byreference to FIGS. 7-8, the FIG. 10 embodiment isolates the pulmonaryvein without also ablating tissue along the lumen or lining of thepulmonary vein or ostium. This is apparent by reference to the resultingcircumferential conduction block 44″ shown in FIG. 11.

[0112] In more detail, FIG. 10 shows a similar device assembly as thatshown in FIGS. 7-8, except that ablation element 308 is adapted toablatively couple with only a circumferential path of tissue along theleft posterior atrial wall which surrounds the pulmonary vein ostium. Inone aspect of this embodiment, the compliant nature of the expandablemember 306 may be self-conforming to the region of the ostium such thatthe ablation element 308 is placed against this atrial wall tissuemerely by way of conformability. FIG. 11 illustrates a circumferentiallesion 44″ formed by the device assembly discussed with reference toFIG. 10. As shown, the circumferential lesion 44″ is located along theposterior wall and does not extend into or around the ostium 54.

[0113] In another aspect of this embodiment, a “pear”-shaped expandablemember or balloon that includes a contoured taper may be suitable foruse according to the FIG. 10 embodiment. Such a pear shape may bepreformed into the expandable member or balloon, or the member may beadapted to form this shape by way of controlled compliance as itexpands, such as for example by the use of composite structures withinthe balloon construction. In any case, according to the “pear”-shapedvariation, the circumferential band of the ablation member is preferablyplaced along the surface of the contoured taper which is adapted to facethe left posterior atrial wall during use according to the methodillustrated by FIG. 10. It is further contemplated that the ablationelement may be further extended or alternatively positioned along otherportions of the taper.

[0114] The method of forming a circumferential conduction block along acircumferential path of tissue along a left posterior atrial wall andwhich surrounds a pulmonary vein ostium without ablating the tissue ofthe vein or ostium should not be limited to the particular deviceembodiments just illustrated by reference to FIG. 10. Other devicevariations may be acceptable substitute for use according to thismethod.

[0115] In one particular example which is believed to be suitable, a“looped” ablation member such as the embodiment illustrated below byreference to FIG. 28 may be adapted to form a “looped” ablation elementwithin the left atrium and then be advanced against the left posterioratrial wall such that the loop engages the circumferential path oftissue along the atrial wall and which surrounds a vein ostium.Thereafter, the looped ablation element may be actuated to ablate theengaged tissue, such as for further illustration like a branding ironforming the predetermined pattern around the pulmonary vein ostium.

[0116] In addition, other device or method variations may also besuitable substitutes according to one of ordinary skill.

Combining Circumferential Lesions with Long Linear Lesions

[0117] FIGS. 12-17 collectively illustrate a circumferential ablationdevice assembly and method as used to form a circumferential lesion incombination with the formation of long linear lesions in a less-invasive“maze”-type procedure, as described above for the treatment ofmultiwavelet reentrant type fibrillation along the left atrial wall. Asdescribed in part by the flow diagram of FIG. 12, the physician may usea linear ablation element to form linear conduction blocks between thepulmonary vein ostia, wherein the circumferential ablation probe of thepresent invention is used to connect the linear lesions by formingcircumferential ablation lesions around the pulmonary vein ostia.

[0118] More specifically, FIG. 12 diagrammatically shows a summary ofsteps for performing a “maze”-type procedure by forming circumferentialconduction blocks that intersect with long linear conduction blocksformed between the pulmonary veins. As disclosed in U.S. Pat. No.5,971,983 to Lesh entitled “Tissue Ablation Device and Method of Use”,which is herein incorporated in its entirety by reference thereto, abox-like conduction block surrounding an arrhythmogenic atrial wallregion bounded by the pulmonary veins may be created by forming longlinear lesions between anchors in all pairs of adjacent pulmonary veinostia. This procedure is summarized in steps (5) and (6) of FIG. 12.However, it is further believed that, in some particular applications,such linear lesions may be made sufficiently narrow with respect to thesurface area of the pulmonary vein ostia that they may not intersect,thereby leaving gaps between them which may present proarrhythmicpathways for abnormal conduction into and from the box. This isillustrated in FIG. 13 by the gaps between lesion 56 and 58 and alsobetween lesions 58 and 60. Therefore, by forming a circumferentialconduction block according to step (7) of FIG. 12, and as shown by useof ablation element 208 in FIG. 14, the linear lesions are therebybridged and the gaps are closed. FIG. 15 illustrates a lesion patternformed by steps (5)-(7) of FIG. 12. With the addition of circumferentiallesion 44′, there are no gaps between the linear lesions and thereforethere are no proarrhythmic pathways for abnormal conduction into and outof the box.

[0119] Moreover, the method shown schematically in FIG. 12 and also invarious detail by reference to FIGS. 13-15 provides a specific sequenceof steps for the purpose of illustration. According to this illustrativesequence, the linear lesions are formed first and then are connectedthereafter with the circumferential conduction block. However, acircumferential conduction block may be formed prior to the formation ofthe linear lesions or conduction blocks, or in any other combination orsub-combination of sequential steps, so long as the resultingcombination of lesions allows for the circumferential block to intersectwith and connect with the linear lesions. In addition, thecircumferential conduction block which connects the linear lesions mayalso include a circumferential path of tissue which surrounds andelectrically isolates the pulmonary vein ostium from the rest of theleft posterior atrial wall.

[0120] In addition to the particular embodiments just shown anddescribed by reference to FIGS. 12-15, other methods are alsocontemplated for combining circumferential and linear conduction blocksdevice assemblies and uses in order to perform a less-invasive“maze”-type procedure. In a further example shown in FIG. 16, anotherlesion pattern is formed by combining the pair of linear lesions of FIG.13 with a circumferential conduction block 44″. While the resultinglesion patterns of FIGS. 15 and 16 differ slightly as regards theparticular geometry and position of the circumferential conduction blockformed, the two variations are also similar in that the circumferentialconduction block includes a circumferential path of atrial wall tissue.When such circumferential conduction blocks are formed between adjacentpulmonary vein ostia, shorter linear lesions are therefore sufficient tobridge the circumferential lesions during the overall “maze”-typeprocedure.

[0121] To this end, according to one contemplated less-invasive“maze”-type procedure (not shown) wherein multiple circumferentialconduction blocks are formed in atrial wall tissue such that eachpulmonary vein ostium is surrounded by and is electrically isolated withone circumferential conduction block. A series of four linear lesionsmay be formed between the various pairs of adjacent ostia and with justsufficient length to intersect with and bridge the correspondingadjacent circumferential blocks. A box-like conduction block is therebyformed by the four circumferential conduction blocks and the fourbridging linear lesions. A fifth linear lesion may be also formedbetween at least a portion of the box-like conduction block and anotherpredetermined location, such as for example the mitral value annulus.

[0122]FIG. 17 schematically illustrates yet a further variation forforming circumferential conduction blocks along atrial wall tissuearound the pulmonary vein ostia during a less invasive “maze”-typeprocedure. According to this further variation, the circumferentialconduction block patterns formed around each of two adjacent superiorand inferior pulmonary vein ostia are shown in FIG. 17 to intersect,thereby alleviating the need for a linear lesion in order to form aconduction block between the ostia. Furthermore, the distances betweenthe inferior and superior ostia, both on the right and left side of theposterior atrial wall, are believed to be significantly shorter than thedistances between the two adjacent superior or inferior ostia.Therefore, FIG. 17 only shows the overlapping circumferential conductionblocks as just described to be positioned vertically between theinferior-superior pairs of adjacent ostia, and further shows linearlesions which are used to connect the right and left sided ostia of thesuperior and inferior pairs. In some instances these linear lesions willnot be required to cure, treat or prevent a particular atrial arrhythmiacondition. However, other combinations of these patterns arefurther-contemplated, such as for example using only overlappingcircumferential conduction blocks between all adjacent pairs of ostia inorder to form the entire “maze”-type left atrial pattern.

Monitoring Electrical Signals During Surgical Procedure

[0123]FIG. 18 diagrammatically shows a further method for using acircumferential ablation device assembly wherein electrical signalsalong the pulmonary vein are monitored with a sensing element before andafter ablation according to steps (8) and (9), respectively. Signalswithin the pulmonary vein are monitored prior to forming a conductionblock, as indicated in step (8) in FIG. 18, in order to confirm that thepulmonary vein chosen contains an arrhythmogenic origin for atrialarrhythmia. Failure to confirm an arrhythmogenic origin in the pulmonaryvein, particularly in the case of a patient diagnosed with focalarrhythmia, may dictate the need to monitor signals in another pulmonaryvein in order to direct treatment to the proper location in the heart.In addition, monitoring the pre-ablation signals may be used to indicatethe location of the arrhythmogenic origin of the atrial arrhythmia,which helps determine the best location to form the conduction block. Assuch, the conduction block may be positioned to include and thereforeablate the actual focal origin of the arrhythmia, or may be positionedbetween the focus and the atrium in order to block aberrant conductionfrom the focal origin and into the atrial wall.

[0124] In addition or in the alternative to monitoring electricalconduction signals in the pulmonary vein prior to ablation, electricalsignals along the pulmonary vein wall may also be monitored by thesensing element subsequent to circumferential ablation, according tostep (9) of the method of FIG. 18. This monitoring method aids intesting the efficacy of the ablation in forming a complete conductionblock against arrhythmogenic conduction. Arrhythmogenic firing from theidentified focus will not be observed during signal monitoring along thepulmonary vein wall when taken below a continuous circumferential andtransmural lesion formation, and thus would characterize a successfulcircumferential conduction block. In contrast, observation of sucharrhythmogenic signals between the lesion and the atrial wallcharacterizes a functionally incomplete or discontinuous circumference(gaps) or depth (transmurality) which would potentially identify theneed for a subsequent follow-up procedure, such as a secondcircumferential lesioning procedure in the ablation region.

[0125] A test electrode may also be used in a “post ablation” signalmonitoring method according to step (10) of FIG. 18. In one particularembodiment not shown, the test electrode is positioned on the distal endportion of a probe shaft and is electrically coupled to a current sourcefor firing a test signal into the tissue surrounding the test electrodewhen it is placed distally or “upstream” of the circumferential lesionin an attempt to simulate a focal arrhythmia. This test signal generallychallenges the robustness of the circumferential lesion in preventingatrial arrhythmia from any such future physiologically generatedaberrant activity along the suspect vein.

[0126] Further to the signal monitoring and test stimulus methods justdescribed, such methods may be performed with a separate electrode orelectrode pair located on the probe distal end portion adjacent to theregion of the circumferential ablation element, or may be performedusing one or more electrodes which form the circumferential ablationelement itself, as will be further developed below.

Surgical Ablation Probe for Forming a Circumferential Lesion

[0127] Circumferential ablation devices disclosed in the past aretranslumenal catheterbased devices that are inserted into a peripheralvein (such as the femoral vein) and are advanced through a guidecatheter into the right atrium and then across the septum into the leftatrium. However, during certain open-heart or minimally invasive cardiacsurgeries, the left atrium may be accessible through an opening in apatient's chest, thereby obviating the need for a catheter-basedapparatus. When the physician can access the left atrium through anopening in a patient's chest, a relatively short and rigid surgicalablation probe is better suited for placing an ablation element in aselected pulmonary vein for the creation of a circumferential lesion.

[0128] With general reference to FIG. 19, a preferred mode of thesurgical ablation probe in accordance with the present invention willnow be described. The surgical ablation probe 100 comprises a handle 120that includes multiple lumens and is ergonomically designed to fitcomfortably in the physician's hand. The handle 120 preferably is madeof a molded or machined plastic. A suitable handle design would besimilar to known handles used on the following types of devices: a laserdevice to perform trans-myocardial revascularization (TMR); a hand-heldRF ablation probe; and a hand-held cryo-ablation probe. In the-case of adeflectable tip version of the probe, several exemplifying types ofcontrol handles are described in U.S. Pat. Nos. 6,024,739 and 5,465,716,which are hereby incorporated by reference.

[0129] The handle 120 supports a multi-lumen probe shaft 102 that isrelatively short in length and is generally rigid. The majority of theshaft 102 is significantly less flexible than the catheter-basedablation devices described in U.S. Pat. No. 6,024,740. The distal end122 preferably includes an atraumatic distal tip 110 made of a softthermoplastic. The shaft 102 preferably has a diameter ranging fromabout 7 to about 12 F. However, this range of diameters merelyexemplifies suitable diameters for use in the described surgicalprocedure, and other diameter probes of course are also within the scopeof the invention.

[0130] The surgical ablation probe 100 also preferably includes sensorleads 148, a power cable 150, preferably a coaxial cable, and actuationmeans 154 for deploying the expandable member 106. These componentsextend from the handle 120, through the lumens in the probe shaft 102,to the corresponding components of the probe disposed on the distal end122. The proximal ends of the cables and lumens connect to correspondingconnectors 153, 155 that extend from the proximal end of the probehandle 120. The probe shaft 102 desirably includes a plurality of lumens(examples of which are illustrated in FIGS. 22-23). Various wires andelectrical leads are routed to the distal end portion 122 through atleast some of these lumens. In a preferred device, these lumensgenerally run the length of the shaft 102; however, for someapplications, the lumens can be shorter.

[0131] The shaft 102 of the surgical ablation probe 100 is preferablyformed with a distal port 158 located distal to the ablation member 104and a proximal port 160 located proximal of the ablation member 104. Thedistal port 158 allows the clinician to introduce fluids into thepatient, take fluid samples from the patient, and take fluid pressurereading on the distal side of the ablation member 104. Similarly, theproximal port 160 allows the clinician to introduce fluids into thepatient, take fluid samples from the patient, and take fluid pressurereading on the proximal side of the ablation member 104. These ports andlumens are particularly useful when pressure or X-ray positioningtechniques are employed, as explained below; however, the probe assembly100 need not include such ports and lumens, such as when only an A-modeor Doppler position monitoring system is used with the probe assembly.

[0132] The probe is primarily designed for use during trans-thoracic(open heart) or minimally invasive cardiac surgery and can be used toform a conduction block during the same surgery in which anotherprocedure is being performed, e.g., when repairing or replacing a mitralvalve. For example, the physician may insert the probe through a chestaccess device, e.g., a trocar, or through an incision during open chestsurgery. As illustrated in FIG. 5, the probe shaft 102 is introducedinto an atrium through an atriotomy 10 in the left atrial appendage, andis then placed at a location where a pulmonary vein extends from theposterior atrial wall. Referring again to FIG. 19, the expandable member106 is then expanded from its collapsed to its expanded state, (e.g., byinflation of a balloon by injection of inflation fluid). Once theexpandable member 106 is positioned, in some cases engaged with, alongthe circumferential region of tissue, the physician actuates theablation element 108 to ablate the region of tissue. During open chestsurgery, the short, rigid, and adjustable nature of the probe shaft 102and handle make placement and ablation more efficient and precise thanwith a translumenal catheter-based apparatus.

[0133] It should be noted that an open-heart procedure would requirecardiopulmonary bypass wherein the patient's blood is diverted andoxygenated by an extracorporeal device. In this case, the atrium andpulmonary vein region will be devoid of blood, flushed clear by saline.This would allow a relatively clear field of view in which to operate.It may be desirable for the entire atrium to be flooded with saline,such that the balloon is engulfed in fluid while inflated. This may helpavoid a “dry interface” between the balloon and the tissue to beablated; such a “dry interface” could be an impediment to ultrasoundenergy conduction into the tissue because ultrasound energy issubstantially reflected by even a thin layer of air.

[0134] Minimally invasive surgical procedures can be performed insimilar fashion, i.e. with cardiopulmonary bypass. On the other hand,minimally invasive cardiac procedures are often done on a “beatingheart”, in which case blood flows normally through the cardiopulmonarysystem. In this case, the probe would be used in an environmentidentical to that of the percutaneous translumenal catheter (i.e. withnormal pulmonary vein/atrial blood flow). In sueh cases, it may benecessary to have a separate visualization system employed to aidplacement of the ablation probe, such as an endoscopic camera,intracardiac ultrasound probe, or fluoroscopic x-ray machine. It mayalso be desirable to include a perfusion lumen (not shown) that extendsbetween ports located proximal and distal to the expandable member.Passive perfusion during expansion of the expandable member is believedto minimize stasis and allow the target pulmonary vein to continue inits atrial filling function during the atrial arrythmia treatementprocedure. Without this perfusion feature, the expandable member blocksthe flow of blood from the vein to the atrium and may result inundesirable thrombogenesis in the pulmonary vein distal to theexpandable member.

[0135]FIG. 21 illustrates an enlarged view of the distal end 122 of theprobe shaft 102. The distal end 122 comprises a circumferential ablationmember 104 having an expandable member 106 and an ablation element 108(shown here as an ultrasound transducer). The expandable member 106 maybe provided with one or more sensors 146 (e.g., temperature sensors orelectrodes) on the exterior portion thereof for providing feedback tothe physician during the ablation procedure.

[0136] The distal end 122 of the shaft 102 is preferably shaped tofacilitate placement initially into the atrium and then into a pulmonaryvein ostium. For example, the distal end may be angled to an angle ofabout 45°. The shaft 102 may have a length ranging from about 20 toabout 60 cm. These lengths and angles, however, only exemplify onepreferred form of the ablation probe 100 that has been found useful fora specific surgical procedure, and other lengths and shapes of the probeare also intended to be within the scope of this invention. In onevariation, the shaft 102 may be shaped, by the physician manipulatingthe shaft, so that the shaft takes on a desired shape. In anothervariation, the probe may have a deflectable distal end which can bedeflected by manipulation of a pull-wire system, as described in furtherdetail below.

[0137] It is also understood that the probe shaft 102 can be configuredfor following different access paths into the atrium, such as, forexample, but without limitation, via a retrograde procedure through themitral valve, transeptally from a right atriotomy, or through a leftatriotomy. The probe shaft 102 may be made of Pebax or any othermaterials that provide adjustable shape, flexibility, andmaneuverability of the probe. Other materials include for example,stainless steel, Nitinol, thermoplastic braided material, polyamidebraided tubing, etc.

[0138]FIG. 20 shows the circumferential ablation probe 100 with theexpandable member 106 in a radially collapsed condition. In thisconfiguration, the ablation probe 100 is adapted for delivery into thepulmonary vein according to positioning step (3) of FIG. 3. Theexpandable member 106 is adjustable to a radially expanded position whenactuated by an expansion actuator 154. In a preferred embodiment, theexpansion actuator 154 comprises a pressurizeable fluid source.

[0139] With reference to FIG. 22, there is shown a cross-sectional viewof the probe shaft 102 taken along line 22-22 of the circumferentialablation probe shown in FIG. 20. An outer extrusion 180 formed of athin-walled, resilient tubing defining the outer surface of the probeshaft 102. The outer extrusion 180 may be formed of any of thebiocompatible resilient plastics typically used in catheters, withpolyimide and polyurethane available under the trade name PEBAX (fromAtochem of Glen Rock, N.J.) being preferred materials.

[0140] Disposed within the outer extrusion 180, and radially outside ofthe inner probe surface 182 is an intermediate layer 184, which isadapted to transmit torque along the probe shaft 102 so that a physiciancan turn the probe distal end portion 152 by suitable manipulation ofthe handle 120. A preferred torque-transmitting material for theintermediate layer 184 is a metal braid formed of interleaved lengths ofstainless steel encapsulated within the resilient plastic outerextrusion 180.

[0141] As illustrated in FIG. 22, several lumens may be disposed withinthe probe shaft 102, including, for example, a deflecting wire lumen198, a coaxial cable lumen 192, a perfusion lumen 196, and athermocouple leads lumen 194. When an inflatable balloon is used as anexpandable member, the probe shaft 102 also includes an inflation lumen190. The inflation lumen 190 preferably has an inner diameter of about0.020 inch in order to allow for rapid deflation times, although thismay vary based upon the viscosity of inflation medium used, length ofthe lumen 190, and other dynamic factors relating to fluid flow andpressure.

[0142] With reference to FIG. 23, there is shown a cross-sectional viewof the probe shaft 102 taken along line 23-23 of the circumferentialablation probe shown in FIG. 20. The same lumens are present within theshaft 102 as described with reference to the proximal region shown inFIG. 22, however, the intermediate, torque-transmitting braid (184 inFIG. 22) is not present within the outer extrusion (180 in FIG. 22).Moreover, the outer extrusion itself is thinner, to reduce the stiffnessof the distal end portion 152. Thus, for illustrative purposes, becauseof the relative thinness of the shaft wall 185 in the distal region, thewall (inner and outer surfaces) is labeled using a single referencenumeral 185.

[0143] Referring now to FIG. 24, a preferred embodiment of the surgicalablation probe 100 further comprises a deflectable tip design toindependently select a desired pulmonary vein and direct the transducerassembly toward the desired location. Further to the deflectablevariation, a deflecting pull wire is incorporated into the probe shaft102. The pull wire is attached to the atraumatic tip 110 of the shaft102, slidably engaged within a pull-wire lumen (198 in FIG. 22 and 23)in the shaft 102, and attached to a deflection mechanism within thehandle 120. The pull wire is adapted to deflect the distal probe tip byapplying tension along varied stiffness transitions along the probe'slength. Still further to this pull wire variation, acceptable pull wiresmay have a diameter within the range from about 0.008 inch to about0.020 inch, and may further include a taper, such as, for example, atapered outer diameter from about 0.020 inch to about 0.008 inch.

[0144] Still referring to FIG. 24, deflection of the distal end 122 ofthe ablation probe 100 is preferably produced by manipulation of a thumbslide 141 located on the handle 120. When the thumb slide 141 is movedfrom position A to position A′ (drawn in phantom), the distal endportion 122 of probe shaft 102 is deflected from position B (zerodeflection) to position B′. Likewise, when the thumb slide 141 is movedfrom position A to position A″ (drawn in phantom), the distal endportion 122 of the shaft 102 is deflected from position B (zerodeflection) to position B″. Although, a variety of deflection handlesare known in the art, they generally operate like the BIOSENSE/WEBSTERhandles by placing tension on the proximal end of a pull wire which isslidably engaged within the probe shaft and fixed to the distal endportion.

[0145]FIG. 25 illustrates an expanded schematic view of one preferredembodiment of the proximal end portion of the probe shaft. It isunderstood, however, that any other extensions and modifications withinthe skill of those in the art are encompassed within the scope of thepresent disclosure. Here, surrounding the proximal end of the probeshaft 102 is a shrink-wrap layer 118, formed from ⅛ inch plasticshrink-wrap, such as for example PET. The inflation lumen is preferablyextended about 16.5 cm using a hypotube 116, preferably of0.042″/0.035″. The coaxial cable 110 extends about 16 cm proximally fromthe proximal end portion 126. A 0.008″ PTFE-coated mandrel was used forthe deflecting pull wire 114, which is shown slidably engaged in a0.026″/0.013″ Teflon tube 112. The Teflon tubing 112 extends only about1 cm past the proximal end portion and the pull wire 114 extends about 4cm beyond the proximal end portion, where it connects to the handle (notshown).

[0146] Referring again to FIG. 19, the circumferential ablation member104 of the probe 100 will be discussed in further detail. The expandablemember 106 of ablation probe 100 preferably comprises a compliantelastomeric balloon or a non-compliant balloon made from silicone,latex, rubber, and polyvinylchloride, with an expandable diameter ofbetween about 10 and about 40 mm. The probe shaft 102 includes aninflation lumen that communicates with the interior of the balloon, andthe handle includes a balloon inflation/deflation port. The port iscoupled to a source of pressurized inflation medium in a known manner toinflate the balloon.

[0147] The ablation element 108 is disposed on the distal tip 122 andcooperates with the expandable member 106 such that the ablation element108 is held in a generally fixed position relative to the targetcircumferential region of tissue. In the preferred embodiment, theablation element 108 is an ultrasound transducer adapted to emitultrasonic sound waves sufficient to ablate a circumferential region oftissue when coupled to a suitable excitation source. It is believed thatdriving the ultrasonic transducer at 20 acoustical watts at an operatingfrequency within the range of 7-10 megahertz will form a sufficientlysized circumfemtial lesion about the pulmonary vein ostium in arelatively short period of time (e.g., 1 to 2 minutes or less).

[0148] The ablation element can be located outside or inside theexpandable member, or can be located at least partially outside theexpandable member. The ablation element, in some forms, also includes aportion of the expandable member. The preferred embodiment illustratedin FIG. 19 shows the ultrasonic transducer 108 located within theexpandable member 106. Electrical-leads extend through lumens in theprobe shaft 102 and connect to one or more electrical connectors thatextend from the probe handle.

[0149] It is also contemplated that the control level of energy can bedelivered, then tested for lesion formation with a test stimulus in thepulmonary vein, either from an electrode provided at the tip area of theprobe or on a separate device. Therefore, the procedure may involveablation at a first energy level in time, then check for the effectiveconductive block provided by the resulting lesion, and then subsequentablations and testing until a complete conductive block is formed.

[0150] In addition to the particular embodiment just described, theultrasonic ablation element and expandable member located at the distalend 122 of the probe shaft 102 can take a variety of otherconfigurations. With regard to the inflatable balloon 106 shown in FIG.19, a central region is generally coaxially disposed over the probeshaft and is bordered at its end neck regions by proximal and distaladaptions. The proximal adaption is sealed over the elongate bodyproximally of the distal inflation and the electrical lead ports and thedistal adaption is sealed over the probe shaft proximal of the distaltip. According to this arrangement, a fluid tight interior chamber isformed within the inflatable balloon 106. This interior chamber isfluidly coupled to a pressurizeable fluid source via the inflation lumenwithin the probe shaft. In addition to the inflation lumen, theelectrical lead lumen also communicates with the interior chamber ofexpandable balloon so that the ultrasound transducer, which ispositioned within that chamber and over the shaft, may be electricallycoupled to the ultrasound drive source or actuator.

[0151] The inflatable balloon 106 may be constructed from a variety ofknown materials, although the balloon preferably is adapted to conformto the contour of a pulmonary vein ostium. For this purpose, the balloonmaterial can be of the highly compliant variety or of a predefinedshape. Because the probe is not restricted in profile as is apercutaneous translumenal catheter, the balloon can have a significantlylarger collapsed profile than the shaft diameter. This allows greaterlatitude in the possible balloon configurations and expanded diameter,including non-compliant balloons, complex shaped balloons, balloons withdramatic surface features such as bumps or ridges, and non-balloonexpandable members. These features may allow treatment of veins withlarge diameter or difficult shape that are not conducive to thelimitations of a percutaneous translumenal catheter design.

[0152] The designs for an expandable member and circumferential ablationelement for use in a circumferential ablation device assembly have beendescribed generically with reference to the embodiments shown in theprevious figures. Examples of more specific expandable member andablation element embodiments which are adapted for use in such ablationdevice assemblies are further provided as follows.

[0153] Notwithstanding their somewhat schematic detail, thecircumferential ablation members shown in the previous figuresillustrate one particular embodiment wherein a circumferential electrodeelement circumscribes an outer surface of an expandable member. Theexpandable member of the embodiments shown may take one of severaldifferent forms, although the expandable member is generally hereinshown as an inflatable balloon that is coupled to an expansion actuator154 and wherein the expansion actuator 154 comprises a pressurizeablefluid source. The balloon is preferably made of a polymeric material andforms a fluid chamber which communicates with a fluid passageway (notshown in the figures) that extends proximally along the elongate probebody and terminates proximally in a proximal fluid port that is adaptedto couple to the pressurizeable fluid source.

[0154] In one expandable balloon variation, the balloon is constructedof relatively inelastic plastics (e.g., polymers or monomers) such as apolyethylene (“PE”; preferably linear low density or high density orblends thereof), polyolefin copolymer (“POC”), polyethylene terepthalate(37 PET”), polyimide, or a nylon material. In this construction, theballoon has a low radial yield or compliance over a working range ofpressures and may be folded into a predetermined configuration whendeflated in order to facilitate introduction of the balloon into thedesired ablation location. In this variation, one balloon size may notsuitably engage all pulmonary vein walls for performing thecircumferential ablation methods herein described on all needy patients.Therefore, it is further contemplated that a kit of multiple ablationprobes, with each balloon working length having a unique predeterminedexpanded diameter, may be provided from which a treating physician maychose a particular device to meet a particular patient's pulmonary veinanatomy.

[0155] In an alternative expandable balloon variation, the balloon isconstructed of a relatively compliant, elastomeric material, such as,for example (but not limited to), a silicone, latex, polyurethane, ormylar elastomer. In this construction, the balloon takes the form of atubular member in the deflated, non-expanded state. When the elastictubular balloon is pressurized with fluid such as in the previous,relatively noncompliant example, the material forming the wall of thetubular member elastically deforms and stretches radially to apredetermined diameter for a given inflation pressure. It is furthercontemplated that the compliant balloon may be constructed as acomposite, such as, for example, a latex or silicone balloon skin whichincludes fibers, such as metal, Kevlar, or nylon fibers, which areembedded into the skin. Such fibers, when provided in a predeterminedpattern such as a mesh or braid, may provide a controlled compliancealong a preferred axis, preferably limiting longitudinal compliance ofthe expandable member while allowing for radial compliance.

[0156] It is believed that, among other features, the relativelycompliant variation may provide a wide range of working diameters, whichmay allow for a wide variety of patients, or of vessels within a singlepatient, to be treated with just one or a few devices. Furthermore, thisrange of diameters is achievable over a relatively low range ofpressures, which is believed to diminish a potentially traumatic vesselresponse that may otherwise be presented concomitant with higherpressure inflations, particularly when the inflated balloon is oversizedto the vessel. In addition, the low-pressure inflation feature of thisvariation is suitable because the functional requirement of theexpandable balloon is merely to engage the ablation element against acircumferential path along the inner lining of the pulmonary vein wall.

[0157] Moreover, a circumferential ablation member is adapted to conformto the geometry of the pulmonary vein ostium, at least in part byproviding substantial compliance to the expandable member, as was shownand described previously by reference to FIGS. 10-11. Further to thisconformability to pulmonary vein ostium as provided in the specificdesign of FIG. 10, the working length L of expandable member 306 is alsoshown to include a taper which has a distally reducing outer diameterfrom a proximal end to a distal end. In either a compliant or thenoncompliant balloon, such a distally reducing tapered geometry adaptsthe circumferential ablation element to conform to the funnelinggeometry of the pulmonary veins in the region of their ostia in order tofacilitate the formation of a circumferential conduction block there.

[0158] The circumferential ablation probe of the present inventionpreferably comprises an ultrasound ablation element for ablating thesurrounding tissue. However, the circumferential ablation probe may beused with a wide variety of ablation elements. For example, in anotherpreferred embodiment, the outer surface of the expandable memberincludes one or more electrode bands adapted to ablatively couple to thesurrounding tissue to form circumferential lesions. The electrode bandsare energized by an ablation actuator that generally includes aradio-frequency (“RF”) current source (not shown) coupled to both the RFelectrode element and also a ground patch 195 which is in skin contactwith the patient to complete an RF circuit. In addition, the ablationactuator preferably includes a monitoring circuit (not shown) and acontrol circuit (not shown) which together use either the electricalparameters of the RF circuit or tissue parameters such as temperature ina feedback control loop to drive current through the electrode elementduring ablation. Also, where a plurality of ablation elements orelectrodes in one ablation element are used, a switching means may beused to multiplex the RF current source between the various elements orelectrodes.

[0159] FIGS. 26A-D show various patterns of electrically conductive,circumferential electrode bands used as electrode ablation elements,each circumscribing an outer surface of the working length of anexpandable member. FIGS. 26A-B show circumferential ablation member 550to include a continuous circumferential electrode band 552 thatcircumscribes an outer surface of an expandable member 570. FIG. 26Bmore specifically shows expandable member 570 as a balloon which isfluidly coupled to a pressurizeable fluid source), and further showselectrode band (circumferential ablation element) 552 electricallycoupled via electrically conductive lead 554 to ablation actuator 156.In addition, a plurality of apertures 572 is shown in the balloon skinwall of expandable member 570 adjacent to electrode band 552. Thepurpose of these apertures 572 is to provide a positive flow of fluidsuch as saline or ringers lactate fluid into the tissue surrounding theelectrode band 552. Such fluid flow is believed to reduce thetemperature rise in the tissue surrounding the electrode element duringRF ablation.

[0160] The shapes shown collectively in FIGS. 26A-D allow for acontinuous electrode band to circumscribe an expandable member's workinglength over a range of expanded diameters, a feature which is believedto be particularly useful with a relatively compliant balloon as theexpandable member. In the particular embodiments of FIGS. 26A-D, thisfeature is provided primarily by a secondary shape given to theelectrode band relative to the longitudinal axis of the working lengthof the expandable member. Electrode band 552 is thus shown in FIGS.26A-B to take the specific secondary shape of a modified step curve.Other shapes than a modified step curve are also suitable, such as theserpentine or sawtooth secondary shapes shown respectively in FIGS.26C-D. Other shapes in addition to those shown in FIGS. 26A-D and whichmeet the defined functional requirements are further contemplated.

[0161] In addition, the electrode band provided by the circumferentialablation elements shown in FIGS. 26C-D has a functional band width wrelative to the longitudinal axis of the working length which is onlyrequired to be sufficiently wide to form a complete conduction blockagainst conduction along the walls of the pulmonary vein in directionsparallel to the longitudinal axis. In contrast, the working length L ofthe respective expandable element is adapted to securely anchor thedistal end portion in place such that the ablation element is firmlypositioned at a selected region of the pulmonary vein for ablation.Accordingly, the band width w is relatively narrow compared to theworking length L of the expandable element, and the electrode band maythus form a relatively narrow equatorial band which has a band widththat is less than two-thirds or even one-half of the working length ofthe expandable element. Additionally, it is to be noted here andelsewhere throughout the specification, that a narrow band may be placedat locations other than the equator of the expandable element,preferably as long as the band is bordered on both sides by a portion ofthe working length L.

[0162] In another aspect of the narrow equatorial band variation for thecircumferential ablation element, the circumferential lesion formed mayalso be relatively narrow when compared to its own circumference, andmay be less than two-thirds or even one-half its own circumference onthe expandable element when expanded. In one arrangement which isbelieved to be suitable for ablating circumferential lesions in thepulmonary veins as conduction blocks, the band width w is less than 1 cmwith a circumference on the working length when expanded that is greaterthan 1.5 cm.

[0163] FIGS. 26E-F show a further variation of a circumferentialablation element which is adapted to maintain a continuouscircumferential lesion pattern over a range of expanded diameters andwhich includes electrode elements that form a relatively narrowequatorial band around the working length of an expandable balloonmember. In this variation, a plurality of individual electrode/ablationelements 562 are included in the circumferential ablation element andare positioned in spaced arrangement along an equatorial band whichcircumscribes an outer surface of the expandable member's working lengthL.

[0164] The size and spacing between these individual electrode elements562, when the balloon is expanded, is adapted to form a substantiallycontinuous circumferential lesion in pulmonary vein wall tissue when inintimal contact adjacent thereto, and is further adapted to form such alesion over a range of band diameters as the working length is adjustedbetween a variety of radially expanded positions. Each individualelectrode element 562 has two opposite ends 563, 564, respectively,along a long axis LA and also has a short axis SA, and is positionedsuch that the long axis LA is at an acute angle relative to thelongitudinal axis LA of the elongate probe body and expandable member560. At least one of the ends 563, 564 along the long axis LA overlapswith an end of another adjacent individual electrode element, such thatthere is a region of overlap along their circumferential aspect, i.e.,there is a region of overlap along the circumferential coordinates. Theterms “region of overlap along their circumferential coordinate” areherein intended to mean that the two adjacent ends each are positionedalong the working length with a circumferential and also a longitudinalcoordinate, wherein they share a common circumferential coordinate. Inthis arrangement, the circumferential compliance along the workinglength, which accompanies radial expansion of the expandable memberalso, moves the individual electrode elements apart along thecircumferential axis. However, the spaced, overlapping arrangementdescribed allows the individual ablation elements to maintain a certaindegree of their circumferential overlap, or at least remain close enoughtogether, such that a continuous lesion may be formed without gapsbetween the elements.

[0165] The construction for suitable circumferential electrode elementsin the RF variations herein described, such as the various electrodeembodiments described with reference to FIGS. 26A-F, may comprise ametallic material deposited on the outer surface of the working lengthusing conventional techniques, such as by plasma depositing, sputtercoating, chemical vapor deposition, other known techniques which areequivalent for this purpose, or otherwise affixing a metallic shapedmember onto the outer surface of the expandable member such as throughknown adhesive bonding techniques. Other RF electrode arrangements arealso considered, so long as they form a circumferential conduction blockas previously described. For example, a balloon skin may itself bemetallized, such as by mixing conductive metal, including but notlimited to gold, platinum, or silver, with a plastic (e.g., polymer) toform a compounded, conductive matrix as the balloon skin.

[0166] Still further to the RF electrode embodiments, anothercircumferential ablation member variation (not shown) may also includean expandable member, such as an inflatable balloon, that includes aporous skin that is adapted to allow fluid, such as hypertonic salinesolution, to pass from an internal chamber defined by the skin andoutwardly into surrounding tissues. Such a porous skin may beconstructed according to several different methods, such as by formingholes in an otherwise contiguous plastic (e.g., polymeric) material,including mechanically drilling or using laser energy, or the porousskin may simply be an inherently porous membrane. In any case, byelectrically coupling the fluid within the porous balloon skin to an RFcurrent source (preferably monopolar), the porous region of theexpandable member serves as an RF electrode wherein RF current flowsoutwardly through the pores via the conductive fluid. In addition, it isfurther contemplated that a porous outer skin may be provided externallyof another, separate expandable member, such as a separate expandableballoon, wherein the conductive fluid is contained in a region betweenthe porous outer skin and the expandable member contained therein.Various other “fluid electrode” designs than those specifically hereindescribed may also be suitable according to one of ordinary skill uponreview of this disclosure.

[0167] In the alternative, or in addition to the RF electrode variationsjust described, the circumferential ablation element may also includeother ablative energy sources or sinks, and particularly may include athermal conductor that circumscribes the outer circumference of theworking length of an expandable member. Examples of suitable thermalconductor arrangements include a metallic element which may, forexample, be constructed as previously described for the more detailed RFembodiments above. However, in the thermal conductor embodiment such ametallic element would be generally either resistively heated in aclosed loop circuit internal to the probe, or conductively heated by aheat source coupled to the thermal conductor. In the latter case ofconductive heating of the thermal conductor with a heat source, theexpandable member may be, for example, a plastic (e.g., polymeric)balloon skin which is inflated with a fluid that is heated either by aresistive coil or by bipolar RF current. In any case, it is believedthat a thermal conductor on the outer surface of the expandable memberis suitable when it is adapted to heat tissue adjacent thereto to atemperature between 40° and 80° Celsius.

[0168] Further to the thermal conduction variation for thecircumferential ablation element, a perfusion balloon embodiment may beparticularly useful in such a design. It is believed that ablationthrough increased temperatures, as provided by example above may alsoenhance coagulation of blood in the pulmonary vein adjacent to theexpandable member, which blood would otherwise remain stagnant withoutsuch a perfusion feature.

[0169] One further circumferential ablation element design which isbelieved to be highly useful in performing the ablation methods hereindescribed is shown in FIG. 27A to include a circumferential ablationmember 600 with two insulators 602, 604 that encapsulate the proximaland distal ends, respectively, of the working length L of an expandablemember 610. In the particular embodiment shown, the insulators 602, 604are thermal insulators, such as a thermal insulator comprising a Teflonmaterial. Expandable member 610 is an inflatable balloon which has aballoon skin 612 that is thermally conductive to surrounding tissue wheninflated with a heated fluid which may contain a radiopaque agent,saline fluid, ringers lactate, combinations thereof, other knownbiocompatible fluids having acceptable heat transfer properties forthese purposes, further to the thermal conductor embodiments previouslydescribed. By providing these spaced insulators, a circumferentialablation element is formed as an equatorial band 603 of uninsulatedballoon skin is located between the opposite insulators. In thisconfiguration, the circumferential ablation element is able to conductheat externally of the balloon skin much more efficiently at theuninsulated equatorial band 603 than at the insulated portions, andthereby is adapted to ablate only a circumferential region of tissue ina pulmonary vein wall which is adjacent to the equatorial band. It isfurther noted that this embodiment is not limited to an “equatorial”placement of the ablation element. Rather, a circumferential band may beformed anywhere along the working length of the expandable member andcircumscribing the longitudinal axis of the expandable member aspreviously described.

[0170]FIG. 27A further shows use of a radiopaque marker 620 to identifythe location of the equatorial band 603 in order to facilitate placementof that band at a selected ablation region of a pulmonary vein via X-rayvisualization. Radiopaque marker 620 is opaque under X-ray, and may beconstructed, for example, of a radiopaque metal such as gold, platinum,or tungsten, or may comprise a radiopaque plastic (e.g., polymer) suchas a metal loaded polymer. Such a radiopaque marker may also be combinedwith the other embodiments herein shown and described. To note, when thecircumferential ablation member which forms an equatorial band includesa metallic electrode element, such electrode may itself be radiopaqueand may not require use of a separate marker as just described.

[0171] The thermal insulator embodiment just described by reference toFIG. 27A is illustrative of a broader embodiment, wherein acircumferential ablation member has an ablating surface along the entireworking length of an expandable member, but is shielded from releasingablative energy into surrounding tissues except for along an unshieldedor uninsulated equatorial band. As such, the insulator embodimentcontemplates other ablation elements, such as the RF embodimentspreviously described above, which are provided along the entire workinglength of an expandable member and which are insulated at their ends toselectively ablate tissue only about an uninsulated equatorial band.

[0172] In a further example using the insulator embodiment incombination with a circumferential RF electrode embodiment, a metallizedballoon which includes a conductive balloon skin may have an electricalinsulator, such as a plastic (e.g., polymeric) coating, at each end ofthe working length and thereby selectively ablate tissue withelectricity flowing through the uninsulated equatorial band. In this andother insulator embodiments, it is further contemplated that theinsulators described may be only partial and still provide theequatorial band result. For instance, in the conductive RF electrodeballoon case, a partial electrical insulator will allow a substantialcomponent of current to flow through the uninsulated portion due to a“shorting” response to the lower resistance in that region.

[0173] In still a further example of an insulator combined with a RFablation electrode, a porous membrane comprises the entire balloon skinof an expandable member. By insulating the proximal and distal endportions of the working length of the expandable member, only the poresin the unexposed equatorial band region are allowed to effuse theelectrolyte which carries an ablative RF current.

[0174] Further to the expandable member design for use in acircumferential ablation member as herein described, other expandablemembers than a balloon are also considered suitable. For example, in oneexpandable cage embodiment shown in FIG. 27B, cage 650 comprisescoordinating wires 651 and is expandable to engage a desired ablationregion in a pulmonary vein.

[0175] The radial expansion of cage 650 is accomplished as follows.Sheath 652 is secured around the wires proximally of cage 650. However,core 653, which may be a metallic mandrel such as stainless steel,extends through sheath 652 and distally within cage 650 wherein itterminates in a distal tip 656. Wires 651 are secured to distal tip 656,for example, by soldering, welding, adhesive bonding, heat shrinking aplastic (e.g., polymeric) member over the wires, or any combination ofthese methods. Core 653 is slidable within sheath 652, and may, forexample, be housed within a tubular lumen (not shown) within sheath 652,the wires being housed between a coaxial space between the tubular lumenand sheath 652. By moving the sheath 652 relative to core 653 and distaltip 656, the cage 650 is collapsible along its longitudinal axis inorder to force an outward radial bias to wires 651 in an organizedfashion to formed a working length of cage 650 which is expanded (notshown).

[0176] Further to the particular expandable cage embodiment shown inFIG. 27B, a plurality of ablation electrodes 655 is shown, each beingpositioned on one of wires 651 and being similarly located along thelongitudinal axis of the cage 650. The radial bias given to wires 651during expansion, together with the location of the ablation electrodes655, serves to position the plurality of ablation electrodes/elements655 along a circumferential, equatorial band along the expanded workinglength of cage 650. The wires forming a cage according to thisembodiment may also have another predetermined shape when in theradially expanded position. For example, a taper similar to that shownfor expandable member 106 in FIG. 19 may be formed by expanding cage650, wherein the ablation element formed by ablation electrodes 655 maybe positioned between the proximal end and the distal end of the taper.

[0177] Further to the construction of the embodiment shown in FIG. 27B,wires 651 are preferably metal, and may comprise stainless steel or asuperelastic metal alloy, such as an alloy of nickel and titanium, or acombination of both. Regarding the case of nickel and titaniumconstruction for wires 655, a separate electrical conductor may berequired in order to actuate ablation electrodes 655 to efficiently emitablative current into surrounding tissues. In the case where wires 651are constructed of stainless steel, they may also serve as electricalconductors for ablation electrodes 655. Further to the stainless steeldesign, the wires 651 may be coated with an electrical insulator toisolate the electrical flow into surrounding tissues at the site of theablation electrodes 655. Moreover, the ablation electrodes 655 in thestainless steel wire variation may be formed simply by removingelectrical insulation in an isolated region to allow for current to flowinto tissue only from that exposed region.

[0178] In a further cage embodiment (not shown) to that shown in FIG.27B, a circumferential strip of electrodes may also be secured to thecage 650 such that the strip circumscribes the cage at a predeterminedlocation along the cage's longitudinal axis. By expanding cage 650 aspreviously described, the strip of electrodes are adapted to take acircumferential shape according to the shape of the expanded cage 650.Such an electrode strip is preferably flexible, such that it may beeasily reconfigured when the cage is adjusted between the radiallycollapsed and expanded positions and such that the strip may be easilyadvanced and withdrawn with the cage within the delivery sheath.Furthermore, the electrode strip may be a continuous circumferentialelectrode such as a conductive spring coil, or may be a flexible stripwhich includes several separate electrodes along its circumferentiallength. In the latter case, the flexible strip may electrically coupleall of the electrodes to a conductive lead that interfaces with a drivecircuit, or each electrode may be separately coupled to one or more suchconductive leads.

[0179] Another circumferential ablation element adapted for use in acircumferential conduction block assembly of the type herein describedis shown in FIG. 28, wherein circumferential ablation member 700includes a looped member 710 attached, preferably by heat shrinking, toa distal end of a pusher 730. Looped member 710 and pusher 730 areslidably engaged within delivery sheath 750 such that looped member 710is in a first collapsed position when positioned and radially confinedwithin delivery sheath 750, and expands to a second expanded positionwhen advanced distally from delivery sheath 750.

[0180] Looped member 710 is shown in more detail in FIG. 28 to include acore 712 which is constructed of a superelastic metal alloy such as anickel-titanium alloy and which has a looped portion with shape memoryin the looped configuration. This looped configuration is shown in FIG.28 to be in a plane which is off-axis, preferably perpendicular, to thelongitudinal axis of the pusher 730. This off-axis orientation of theloop is adapted to engage a circumferential path of tissue along apulmonary vein wall which circumscribes the pulmonary vein lumen whenthe looped member 710 is delivered from the delivery sheath 750 when thedelivery sheath is positioned within the vein lumen parallel to itslongitudinal axis. An ablation electrode 714 is also shown in FIG. 28 asa metallic coil which is wrapped around core 712 in its looped portion.

[0181] Pusher 730 is further shown in FIG. 28 to include a tubularpusher member 732 which is heat shrunk over two ends 712′ of core 712which extend proximally of looped member 710 through pusher 730 in theparticular variation shown. While in this embodiment core 712 extendsthrough the pusher in order to provide stiffness to the composite designfor the pusher, it is further contemplated that the superelastic metalof the core may be replaced or augmented in the pusher region withanother different mandrel or pusher core (not shown), such as a stifferstainless steel mandrel. Also shown within pusher 730 is an electricallyconductive lead 735 which is coupled to the ablation electrode 714 andwhich is also adapted in a proximal region of the pusher (not shown) tocouple to an ablation actuator 156 such as an RF current source (shownschematically).

[0182] FIGS. 29A-31B show various specific embodiments of a broadercircumferential ablation device assembly which utilizes an ultrasonicenergy source to ablate tissue. The present circumferential ablationdevice has particular utility in connection with forming acircumferential lesion within or about a pulmonary vein ostium or withinthe vein itself in order to form a circumferential conductive block.This application of the present ablation device, however, is merelyexemplary, and it is understood that those skilled in the art canreadily adapt the present ablation device for applications in other bodyspaces.

[0183] As common to each of the following embodiments, a source ofacoustic energy is provided for a delivery device that also includes ananchoring mechanism. In one mode, the anchoring mechanism comprises anexpandable member that also positions the acoustic energy source withinthe body; however, other anchoring and positioning devices may also beused, such as, for example, a basket mechanism. In a more specific form,the acoustic energy source is located within the expandable member andthe expandable member is adapted to engage a circumferential path oftissue either about or along a pulmonary vein in the region of itsostium along a left atrial wall. The acoustic energy source in turn isacoustically coupled to the wall of the expandable member and thus tothe circumferential region of tissue engaged by the expandable memberwall by emitting a circumferential and longitudinally collimatedultrasound signal when actuated by an acoustic energy driver. The use ofacoustic energy, and particularly ultrasonic energy, offers theadvantage of simultaneously applying a dose of energy sufficient toablate a relatively large surface area within or near the heart to adesired heating depth without exposing the heart to a large amount ofcurrent. For example, a collimated ultrasonic transducer can form alesion, which has about a 1.5 mm width, about a 2.5 mm diameter lumen,such as a pulmonary vein and of a sufficient depth to form an effectiveconductive block. It is believed that an effective conductive block canbe formed by producing a lesion within the tissue that is transmural orsubstantially transmural. Depending upon the patient as well as thelocation within the pulmonary vein ostium, the lesion may have a depthof 1 millimeter to 10 millimeters. It has been observed that thecollimated ultrasonic transducer can be powered to provide a lesionhaving these parameters so as to form an effective conductive blockbetween the pulmonary vein and the posterior wall of the left atrium.

[0184] With specific reference now to the embodiment illustrated inFIGS. 29A through 29D, a circumferential ablation device assembly 800includes a shaft 802 with proximal and distal end portions 810,812, anexpandable balloon 820 located along the distal end portion 812 ofelongate body 802, and a circumferential ultrasound transducer 830 whichforms a circumferential ablation member which is acoustically coupled tothe expandable balloon 820. In more detail, FIGS. 29A-C variously showshaft 802 to include inflation lumen 806 and electrical lead lumen 808.

[0185] Each lumen extends between a proximal port (not shown) and arespective distal port, which distal ports are shown as distal inflationport 807 for inflation lumen 806, and distal lead port 809 forelectrical lead lumen 808. Although the inflation and electrical leadlumens are generally arranged in a side-by-side relationship, theelongate body 802 can be constructed with one or more of these lumensarranged in a coaxial relationship, or in any of a wide variety ofconfigurations that will be readily apparent to one of ordinary skill inthe art.

[0186] In addition, the shaft 802 is also shown in FIGS. 29A and 29C toinclude an inner member 803 which extends distally beyond distalinflation and lead ports 807, 809, through an interior chamber formed bythe expandable balloon 820, and distally beyond expandable balloon 820where the shaft terminates in a distal tip. The inner member 803provides a support member for the cylindrical ultrasound transducer 830and for the distal neck of the expansion balloon, as described in moredetail below.

[0187] In addition to providing the requisite lumens and support membersfor the ultrasound transducer assembly, the shaft 802 of the presentembodiment must also be adapted to be introduced into the left atriumsuch that the distal end portion with balloon and transducer may beplaced within the pulmonary vein ostium. Therefore, the distal endportion 812 is preferably flexible. In one further more detailedconstruction which is believed to be suitable, the proximal end portionis adapted to be at least 30% more stiff than the distal end portion.According to this relationship, the proximal end portion may be suitablyadapted to provide push transmission to the distal end portion while thedistal end portion is suitably adapted to track through bending anatomyduring in vivo delivery of the distal end portion of the device into thedesired ablation region.

[0188] The body may also comprise a “pullwire” lumen and associatedfixed pullwire which is adapted to deflect the probe tip by applyingtension along varied stiffness transitions along the probe's length.Still further to this pullwire variation, acceptable pullwires may havea diameter within the range from about 0.008 inch to about 0.020 inch,and may further include a taper, such as, for example, a tapered outerdiameter from about 0.020 inch to about 0.008 inch.

[0189] More specifically regarding expandable balloon 820 as shown invaried detail between FIGS. 29A and 29C, a central region 822 isgenerally coaxially disposed over the inner member 803 and is borderedat its end neck regions by proximal and distal adaptions 824, 826. Theproximal adaption 824 is sealed over shaft 802 proximally of the distalinflation and the electrical lead ports 807,809, and the distal adaption826 is sealed over inner member 803. According to this arrangement, afluid tight interior chamber is formed within expandable balloon 820.This interior chamber is fluidly coupled to a pressurizeable fluidsource (not shown) via inflation lumen 806. In addition to the inflationlumen 806, electrical lead lumen 808 also communicates with the interiorchamber of expandable balloon 820 so that the ultrasound transducer 830,which is positioned within that chamber and over the inner member 803,may be electrically coupled to an ultrasound drive source or actuator,as will be provided in more detail below.

[0190] The expandable balloon 820 may be constructed from a variety ofknown materials, although the balloon 820 preferably is, adapted toconform to the contour of a pulmonary vein ostium. For this purpose, theballoon material can be of the highly compliant Variety, such that thematerial elongates upon application of pressure and takes on the shapeof the body lumen or space when fully inflated. Suitable balloonmaterials include elastomers, such as, for example, but withoutlimitation, Silicone, latex, or low durometer polyurethane (for example,a durometer of about 80A).

[0191] In addition or in the alternative to constructing the balloon ofhighly compliant material, the balloon 820 can be formed to have apredefined fully inflated shape (i.e., be preshaped) to generally matchthe anatomic shape of the body lumen in which the balloon is inflated.For instance, as described below in greater detail, the balloon can havea distally tapering shape to generally match the shape of a pulmonaryvein ostium, and/or can include a bulbous proximal end to generallymatch a transition region of the atrium posterior wall adjacent to thepulmonary vein ostium. In this manner, the desired seating within theirregular geometry of a pulmonary vein or vein ostium can be achievedwith both compliant and non-compliant balloon variations.

[0192] Notwithstanding the alternatives which may be acceptable as justdescribed, the balloon 820 is preferably constructed to exhibit at least300% expansion at 3 atmospheres of pressure, and more preferably toexhibit at least 400% expansion at that pressure. The term “expansion”is herein intended to mean the balloon outer diameter afterpressurization divided by the balloon inner diameter beforepressurization, wherein the balloon inner diameter before pressurizationis taken after the balloon is substantially filled with fluid in ataught configuration. In other words, “expansion” is herein intended torelate to change in the diameter that is attributable to the materialcompliance in a stress strain relationship. In one more detailedconstruction which is believed to be suitable for use in most conductionblock procedures in the region of the pulmonary veins, the balloon isadapted to expand under a normal range of pressure such that its outerdiameter may be adjusted from a radially collapsed position of about 5millimeters to a radially expanded position of about 2.5 centimeters (orapproximately 500% expansion ratio).

[0193] The ablation member, which is illustrated in FIGS. 30A-D, takesthe form of annular ultrasonic transducer 830. In the illustratedembodiment, the annular ultrasonic transducer 830 has a unitarycylindrical shape with a hollow interior (i.e., is tubular shaped);however, the transducer applicator 830 can have a generally annularshape and be formed of a plurality of segments. For instance, thetransducer applicator 830 can be formed by a plurality of tube sectorsthat together form an annular shape. The tube sectors can also be ofsufficient arc lengths so as when joined together, the sectors assemblyforms a “clover-leaf” shape. This shape is believed to provide overlapin heated regions between adjacent elements. The generally annular shapecan also be formed by a plurality of planar transducer segments whichare arranged in a polygon shape (e.g., hexagon). In addition, althoughin the illustrated embodiment the ultrasonic transducer comprises asingle transducer element, the transducer applicator can be formed of amulti-element array, as described in greater detail below.

[0194] Cylindrical ultrasound transducer 830 includes a tubular wall 831which includes three concentric tubular layers. The central layer 832 isa tubular shaped member of a piezoceramic or piezoelectric crystallinematerial. The transducer preferably is made of type PZT-4, PZT-5 orPZT-8, quartz or Lithium-Niobate type piezoceramic material to ensurehigh power output capabilities. These types of transducer materials arecommercially available from Stavely Sensors, Inc. of East Hartford,Conn., or from Valpey-Fischer Corp. of Hopkinton, Mass.

[0195] The outer and inner tubular members 833, 834 enclose centrallayer 832 within their coaxial space and are constructed of anelectrically conductive material. In the illustrated embodiment, thesetransducer electrodes 833, 834 comprise a metallic coating, and morepreferably a coating of nickel, copper, silver, gold, platinum, oralloys of these metals.

[0196] One more detailed construction for a cylindrical ultrasoundtransducer for use in the present application is as follows. The lengthof the transducer 830 or transducer assembly (e.g., multi-element arrayof transducer elements) desirably is selected for a given clinicalapplication. In connection with forming circumferential condition blocksin cardiac or pulmonary vein wall tissue, the transducer length can fallwithin the range of approximately 2 mm up to greater than 10 mm, andpreferably equals about 5 mm to 10 mm. A transducer accordingly sized isbelieved to form a lesion of a width sufficient to ensure the integrityof the formed conductive block without undue tissue ablation. For otherapplications, however, the length can be significantly longer.

[0197] Likewise, the transducer outer diameter desirably is selected toaccount for delivery through a particular access path (e.g.,percutaneously and transeptally), for proper placement and locationwithin a particular body space, and for achieving a desired ablationeffect. In the given application within or proximate of the pulmonaryvein ostium, the transducer 830 preferably has an outer diameter withinthe range of about 1.8 mm to greater than 2.5 mm. It has been observedthat a transducer with an outer diameter of about 2 mm generatesacoustic power levels approaching 20-50 Watts per centimeter radiator orgreater within myocardial or vascular tissue, which is believed to besufficient for ablation of tissue engaged by the outer balloon for up toabout 2 cm outer diameter of the balloon. For applications in other bodyspaces, the transducer applicator 830 may have an outer diameter withinthe range of about 1mm to greater than 3-4 mm (e.g., as large as 1 to 2cm for applications in some body spaces).

[0198] The central layer 832 of the transducer 830 has a thicknessselected to produce a desired operating frequency. The operatingfrequency will vary of course depending upon clinical needs, such as thetolerable outer diameter of the ablation and the depth of heating, aswell as upon the size of the transducer as limited by the delivery pathand the size of the target site. As described in greater detail below,the transducer 830 in the illustrated application preferably operateswithin the range of about 5 MHz to about 30 MHz, and more preferablywithin the range of about 7 MHz to about 10 MHz. Thus, for example, thetransducer can have a thickness of approximately 0.3 mm for an operatingfrequency of about 7 MHz (i.e., a thickness generally equal to ½ thewavelength associated with the desired operating frequency).

[0199] The transducer 830 is vibrated across the wall thickness and toradiate collimated acoustic energy in the radial direction. For thispurpose, as best seen in FIGS. 30A and 30D, the distal ends ofelectrical leads 836, 837 are electrically coupled to outer and innertubular members or electrodes 833, 834, respectively, of the transducer830, such as, for example, by soldering the leads to the metalliccoatings or by resistance welding. In the illustrated embodiment, theelectrical leads are 4-8 mil (0.004 to 0.008 inch diameter) silver wireor the like.

[0200] The proximal ends of these leads are adapted to couple to anultrasonic driver or actuator 840, which is schematically illustrated inFIG. 29D. FIGS. 29A-D further show leads 836, 837 as separate wireswithin electrical lead lumen 808, in which configuration the leads mustbe well insulated when in close contact. Other configurations for leads836, 837 are therefore contemplated. For example, a coaxial cable mayprovide one cable for both leads which is well insulated as toinductance interference. Or, the leads may be communicated toward thedistal end portion 812 of the elongate body through different lumenswhich are separated by the probe body.

[0201] The transducer also can be sectored by scoring or notching theouter transducer electrode 833 and part of the central layer 832 alonglines parallel to the longitudinal axis L of the transducer 830, asillustrated in FIG. 29E. A separate electrical lead connects to eachsector in order to couple the sector to a dedicated power control thatindividually excites the corresponding transducer sector. By controllingthe driving power and operating frequency to each individual sector, theultrasonic driver 840 can enhance the uniformity of the ultrasonic beamaround the transducer 830, as well as can vary the degree of heating(i.e., lesion control) in the angular dimension.

[0202] The ultrasound transducer just described is combined with theoverall device assembly according to the present embodiment as follows.In assembly, the transducer 830 desirably is “air-backed” to producemore energy and to enhance energy distribution uniformity, as known inthe art. In other words, the inner member 803 does not contact anappreciable amount of the inner surface of transducer inner tubularmember 834. This is because the piezoelectric crystal which formscentral layer 832 of ultrasound transducer 830 is adapted to radiallycontract and expand (or radially “vibrate”) when an alternating currentis applied from a current source and across the outer and inner tubularelectrodes 833, 834) of the crystal via the electrical leads 836, 837.This controlled vibration emits the ultrasonic energy which is adaptedto ablate tissue and form a circumferential conduction block accordingto the present embodiment. Therefore, it is believed that appreciablelevels of contact along the surface of the crystal may provide adampening effect which would diminish the vibration of the crystal andthus limit the efficiency of ultrasound transmission.

[0203] For this purpose, the transducer 830 seats coaxial about theinner member 803 and is supported about the inner member 803 in a mannerproviding a gap between the. inner member 803 and the transducer innertubular member 834. That is, the inner tubular member 834 forms aninterior bore 835 which loosely receives the inner member 803. Any of avariety of structures can be used to support the transducer 830 aboutthe inner member 803. For instance, spacers or splines can be used tocoaxially position the transducer 830 about the inner member 803 whileleaving a generally annular space between these components. In thealternative, other conventional and known approaches to support thetransducer can also be used. For instance, O-rings that circumscribe theinner member 803 and lie between the inner member 803 and the transducer830 can support the transducer 830 in a manner similar to thatillustrated in U.S. Pat. Nos. 5,606,974; 5,620,479; and 5,606,974, thedisclosures of which were previously incorporated by reference above.

[0204] In a further mode, the probe shaft 802 can also includeadditional lumens which lie either side by side to or coaxial, whichterminate at ports located within the space between the inner member 803and the transducer 830. A cooling medium can circulate through spacedefined by the stand-off 838 between the inner member 803 and thetransducer 830 via these additional lumens. By way of example, carbondioxide gas, circulated at a rate of 5 liters per minute, can be used asa suitable cooling medium to maintain the transducer at a loweroperating temperature. It is believed that such thermal cooling wouldallow more acoustic power to transmit to the targeted tissue withoutdegradation of the transducer material.

[0205] The transducer 830 desirably is electrically and mechanicallyisolated from the interior of the balloon 820. Again, any of a varietyof coatings, sheaths, sealants, tubings and the like may be suitable forthis purpose, such as those described in U.S. Pat. Nos. 5,620,479 and5,606,974. In the illustrated embodiment, as best illustrated in FIG.30C, a conventional, flexible, acoustically compatible, and medicalgrade epoxy 842 is applied over the transducer 830. The epoxy 842 maybe, for example, Epotek 301, Epotek 310, which is available commerciallyfrom Epoxy Technology, or Tracon FDA-8. In addition, a conventionalsealant, such as, for example, General Electric Silicone II gasket glueand sealant, desirably is applied at the proximal and distal ends of thetransducer 830 around the exposed portions of the inner member 803,wires 836, 837 and stand-off 838 to seal the space between thetransducer 830 and the inner member 803 at these locations.

[0206] An ultra thin-walled polyester heat shrink tubing 844 or the likethen seals the epoxy coated transducer. Alternatively, the epoxy coveredtransducer 830, inner member 803 and stand-off 838 can be insteadinserted into a tight thin wall rubber or plastic tubing made from amaterial such as Teflon®, polyethylene, polyurethane, silastic or thelike. The tubing desirably has a thickness of 0.0005 to 0.003 inches.

[0207] When assembling the ablation device assembly, additional epoxy isinjected into the tubing after the tubing is placed over the epoxycoated transducer 830. As the tube shrinks, excess epoxy flows out and athin layer of epoxy remains between the transducer and the heat shrinktubing 844. These layers 842, 844 protect the transducer surface, helpacoustically match the transducer 830 to the load, makes the ablationdevice more robust, and ensures air-tight integrity of the air backing.

[0208] Although not illustrated in FIG. 29A in order to simplify thedrawing, the tubing 844 extends beyond the ends of transducer 830 andsurrounds a portion of the inner member 803 on either side of thetransducer 830. A filler (not shown) can also be used to support theends of the tubing 844. Suitable fillers include flexible materials suchas, for example, but without limitation, epoxy, Teflong tape and thelike.

[0209] The ultrasonic actuator 840 generates alternating current topower the transducer 830. The ultrasonic actuator 840 drives thetransducer 830 at frequencies within the range of about 5 to about 50MHz, and preferably for the illustrated application within the range ofabout 7 MHz to about 10 MHz. In addition, the ultrasonic driver canmodulate the driving frequencies and/or vary power in order to smooth orunify the produced collimated ultrasonic beam. For instance, thefunction generator of the ultrasonic actuator 840 can drive thetransducer at frequencies within the range of 6.8 MHz and 7.2 MHz bycontinuously or discretely sweeping between these frequencies.

[0210] The ultrasound transducer 830 of the present embodiment sonicallycouples with the outer skin of the balloon 820 in a manner which forms acircumferential conduction block in a pulmonary vein as follows.Initially, the ultrasound transducer is believed to emit its energy in acircumferential pattern which is highly collimated along thetransducer's length relative to its longitudinal axis L (see FIG. 30D).The circumferential band therefore maintains its width andcircumferential pattern over an appreciable range of diameters away fromthe source at the transducer. Also, the balloon is preferably inflatedwith fluid which is relatively ultrasonically transparent, such as, forexample, degassed water. Therefore, by actuating the transducer 830while the balloon 820 is inflated, the circumferential band of energy isallowed to translate through the inflation fluid and ultimatelysonically couple with a circumferential band of balloon skin whichcircumscribes the balloon 820. Moreover, the circumferential band ofballoon skin material may also be further engaged along acircumferential path of tissue which circumscribes the balloon, such as,for example, if the balloon is inflated within and engages a pulmonaryvein wall, ostium, or region of atrial wall. Accordingly, where theballoon is constructed of a relatively ultrasonically transparentmaterial, the circumferential band of ultrasound energy is allowed topass through the balloon skin and into the engaged circumferential pathof tissue such that the circumferential path of tissue is ablated.

[0211] Further to the transducer-balloon relationship just described,the energy is coupled to the tissue largely via the inflation fluid andballoon skin. It is believed that, for in vivo uses, the efficiency ofenergy coupling to the tissue, and therefore ablation efficiency, maysignificantly diminish in circumstances where there is poor contact andconforming interface between the balloon skin and the tissue.Accordingly, it is contemplated that several different balloon types maybe provided for ablating different tissue structures so that aparticular shape may be chosen for a particular region of tissue to beablated.

[0212] In one particular balloon-transducer combination shown in FIG.29A and also in FIG. 31A, the ultrasound transducer preferably has alength such that the ultrasonically coupled band of the balloon skin,having a similar length d according to the collimated ultrasound signal,is shorter than the working length D of the balloon. According to thisaspect of the relationship, the transducer is adapted as acircumferential ablation member which is coupled to the balloon to forman ablation element along a circumferential band of the balloon,therefore forming a circumferential ablation element band whichcircumscribes the balloon. Preferably, the transducer has a length whichis less than two-thirds the working length of the balloon, and morepreferably is less than one-half the working length of the balloon. Bysizing the ultrasonic transducer length d smaller than the workinglength D of the balloon 820—and hence shorter than a longitudinal lengthof the engagement area between the balloon 820 and the wall of the bodyspace (e.g., pulmonary vein ostium)—and by generally centering thetransducer 830 within the balloon's working length D, the transducer 830operates in a field isolated from the blood pool. A generally equatorialposition of the transducer 830 relative to the ends of the balloon'sworking length also assists in the isolation of the transducer 830 fromthe blood pool. It is believed that the transducer placement accordingto this arrangement may be preventative of thrombus formation whichmight otherwise occur at a lesion sight, particularly in the leftatrium.

[0213] The ultrasound transducer described in various levels of detailabove has been observed to provide a suitable degree of radiopacity forlocating the energy source at a desired location for ablating theconductive block. However, it is further contemplated that the probeshaft 802 may include an additional radiopaque marker or markers (notshown) to identify the location of the ultrasonic transducer 830 inorder to facilitate placement of the transducer at a selected ablationregion of a pulmonary vein via X-ray visualization. The radiopaquemarker is opaque under X-ray, and can be constructed, for example, of aradiopaque metal such as gold, platinum, or tungsten, or can comprise aradiopaque plastic (e.g., polymer) such as a metal loaded polymer. Theradiopaque marker is positioned coaxially over an inner tubular member803.

[0214] The present circumferential ablation device is introduced into apulmonary vein of the left atrium in a manner similar to that describedpreviously. Once properly positioned within the pulmonary vein or veinostium, the pressurized fluid source inflates the balloon 820 to engagethe lumenal surface of the pulmonary vein ostium. Once properlypositioned, the ultrasonic driver 840 is energized to drive thetransducer 830. It is believed that by driving the ultrasonic transducer830 at 20 acoustical watts at an operating frequency of 7 megahertz,that a sufficiently sized lesion can be formed circumferentially aboutthe pulmonary vein ostium in a relatively short period of time (e.g., 1to 2 minutes or less). It is also contemplated that the control level ofenergy can be delivered, then tested for lesion formation with a teststimulus in the pulmonary vein, either from an electrode provided at thetip area of the ultrasonic probe or on a separate device. Therefore, theprocedure may involve ablation at a first energy level in time, thencheck for the effective conductive block provided by the resultinglesion, and then subsequent ablations and testing until a completeconductive block is formed. In the alternative, the circumferentialablation device may also include feedback control, for example, ifthermocouples are provided at the circumferential element formed alongthe balloon outer surface. Monitoring temperature at this locationprovides indicia for the progression of the lesion. This feedbackfeature may be used in addition to or in the alternative to themulti-step procedure described above.

[0215] FIGS. 30A-C show various alternative designs for the purpose ofillustrating the relationship between the ultrasound transducer andballoon of the assemblies just described above. More specifically, FIG.30A shows the balloon 820 having “straight” configuration with a workinglength L and a relatively constant diameter X between proximal anddistal tapers 824, 826. As is shown in FIG. 30A, this variation isbelieved to be particularly well adapted for use in forming acircumferential conduction block along a circumferential path of tissuewhich circumscribes and transects a pulmonary vein wall. However, unlessthe balloon is constructed of a material having a high degree ofcompliance and conformability, this shape may provide for gaps incontact between the desired circumferential band of tissue and thecircumferential band of the balloon skin along the working length of theballoon 820.

[0216] The balloon 820 in FIG. 30A is also concentrically positionedrelative to the longitudinal axis of the probe shaft 802. It isunderstood, however, that the balloon can be asymmetrically positionedon the elongate body, and that the ablation device can include more thanone balloon.

[0217]FIG. 30B shows another circumferential ablation device assemblyfor pulmonary vein isolation, although this assembly includes a balloon820 which has a tapered outer diameter from a proximal outer diameter X₂to a smaller distal outer diameter X₁. (Like reference numerals havebeen used in each of these embodiments in order to identify generallycommon elements between the embodiments.) According to this mode, thistapered shape is believed to conform well to other tapering regions ofspace, and may also be particularly beneficial for use in engaging andablating circumferential paths of tissue along a pulmonary vein ostium.

[0218]FIG. 30C further shows a similar shape for the balloon as thatjust illustrated by reference to FIG. 30B, except that the FIG. 30Cembodiment further includes a balloon 820 and includes a bulbousproximal end 846. In the illustrated embodiment, the proximate bulbousend 846 of the central region 822 gives the balloon 820 a “pear”-shape.More specifically, a contoured surface 848 is positioned along thetapered working length L and between proximal shoulder 824 and thesmaller distal shoulder 826 of balloon 820. As is suggested by view ofFIG. 30C, this pear shaped embodiment is believed to be beneficial forforming the circumferential conduction block along a circumferentialpath of atrial wall tissue which surrounds and perhaps includes thepulmonary vein ostium. For example, the device shown in FIG. 30C isbelieved to be suited to form a similar lesion to that shown atcircumferential lesion 850 in FIG. 30D. Circumferential lesion 850electrically isolates the respective pulmonary vein 852 from asubstantial portion of the left atrial wall. The device shown in FIG.30C is also believed to be suited to form an elongate lesion whichextends along a substantial portion of the pulmonary vein ostium 854,e.g., between the proximal edge of the illustrated lesion 850 and thedashed line 856 which schematically marks a distal edge of such anexemplary elongate lesion 850.

[0219] As mentioned above, the transducer 830 can be formed of an arrayof multiple transducer elements that are arranged in series and coaxial.The transducer can also be formed to have a plurality of longitudinalsectors. These modes of the transducer have particular utility inconnection with the tapering balloon designs illustrated in FIGS. 30Band 30C. In these cases, because of the differing distances along thelength of the transducer between the transducer and the targeted tissue,it is believed that a non-uniform heating depth could occur if thetransducer were driven at a constant power. In order to uniformly heatthe targeted tissue along the length of the transducer assembly, morepower may therefore be required at the proximal end than at the distalend because power falls off as 1/radius from a source (i.e., from thetransducer) in water. Moreover, if the transducer 830 is operating in anattenuating fluid, then the desired power level may need to account forthe attenuation caused by the fluid. The region of smaller balloondiameter near the distal end thus requires less transducer power outputthan the region of larger balloon diameter near the proximal end.Further to this premise, in a more specific embodiment transducerelements or sectors, which are individually powered, can be provided andproduce a tapering ultrasound power deposition. That is, the proximaltransducer element or sector can be driven at a higher power level thanthe distal transducer element or sector so as to enhance the uniformityof heating when the transducer lies skewed relative to the target site.

[0220] The circumferential ablation device 800 can also includeadditional mechanisms to control the depth of heating. For instance, theprobe shaft 802 can include an additional lumen which is arranged on thebody so as to circulate the inflation fluid through a closed system,such as a heat exchanger. A heat exchanger can remove heat from theinflation fluid and the flow rate through the closed system can becontrolled to regulate the temperature of the inflation fluid. Thecooled inflation fluid within the balloon 820 can thus act as a heatsink to conduct away some of the heat from the targeted tissue andmaintain the tissue below a desired temperature (e.g., 90 decrees C),and thereby increase the depth of heating. That is, by maintaining thetemperature of the tissue at the balloon/tissue interface below adesired temperature, more power can be deposited in the tissue forgreater penetration. Conversely, the fluid can be allowed to warm. Thisuse of this feature and the temperature of the inflation fluid can bevaried from procedure to procedure, as well as during a particularprocedure, in order to tailor the degree of ablation to a givenapplication or patient.

[0221] The depth of heating can also be controlled by selecting theinflation material to have certain absorption characteristics. Forexample, by selecting an inflation material with higher absorption thanwater, less energy will reach the balloon wall, thereby limiting thermalpenetration into the tissue. It is believed that the following fluidsmay be suitable for this application: vegetable oil, silicone oil andthe like.

[0222] Uniform heating can also be enhanced by rotating the transducerwithin the balloon. For this purpose, the transducer 830 may be mountedon a torquable member which is movably engaged within a lumen that isformed by the probe shaft 802.

[0223] In general as to the variations embodied by those figures, thecircumferential ultrasound energy signal is modified at the ballooncoupling level such that a third order of control is provided for thetissue lesion pattern (the first order of control is the transducerproperties affecting signal emission, such as length, width, shape ofthe transducer crystal; the second order of control for tissue lesionpattern is the balloon shape, per above by reference to FIGS. 30A-C).

[0224] Another aspect of the balloon-transducer relationship of thepresent embodiment is illustrated by reference to FIGS. 31A-B. Ingeneral, as to the variations embodied by those Figures, thecircumferential ultrasound energy signal is modified at the ballooncoupling level such that a third order of control is provided for thetissue lesion pattern (the first order of control is the transducerproperties affecting signal emission, such as length, width, shape ofthe transducer crystal; the second order of control for tissue lesionpattern is the balloon shape, per above by reference to FIGS. 30A-C).

[0225] This third order of control for the tissue lesion pattern can beunderstood more particularly with reference to FIG. 31A, which showsballoon 820 to include a shield or filter 860. The filter 860 has apredetermined pattern along the balloon surface adapted to shield tissuefrom the ultrasound signal, for example, by either absorbing orreflecting the ultrasound signal. In the particular variation shown inFIG. 31A, the filter 860 is patterned so that the energy band which ispassed through the balloon wall is substantially more narrow than theband that emits from the transducer 830 internally of the balloon 820.The filter 860 can be constructed, for example, by coating the balloon820 with an ultrasonically reflective material, such as with a metal, orwith an ultrasonically absorbent material, such as with a polyurethaneelastomer. Or, the filter can be formed by varying the balloon's wallthickness such that a circumferential band 862, which is narrow in thelongitudinal direction as compared to the length of the balloon, is alsothinner (in a radial direction) than the surrounding regions, therebypreferentially allowing signals to pass through the band 862. Thethicker walls of the balloon 820 on either side of the band 862 inhibitpropagation of the ultrasonic energy through the balloon skin at theselocations.

[0226] That is, the disclosed modes of suspension maintain an air gapbetween the transducer and the probe shaft. As mentioned above, airbacking of a cylindrical acoustic transducer is desirable to ensuremaximum radially outward propagation of the ultrasound waves. While thetransducer is damped whenever it is in contact with any sort of mountingmeans between the back or inner side of the transducer and the probeshaft, even highly elastomeric ones, the disclosed designs of theseFigures are constructed to minimize such damping. In addition, the airspace desirably is sealed to prevent fluid infiltration, be it blood orwater. These features are common to the following constructionvariations.

[0227] In each of the variations disclosed below, the transducer isconstructed for use in applications involving forming a circumferentiallesion at a base of or in a pulmonary vein to treat atrial fibrillationas described above. In this application, the transducer preferably isdriven in a range of about 6 to about 12 MHz. The transducer for thispurpose can have a thickness in the range of about 0.009 (0.23 mm) toabout 0.013 inches (0.33 mm). For example, a preferred transducer inaccordance with the suspended coaxial transducer embodiment may have aninner diameter of 0.070 inch (1.8 mm) and an outer diameter of 0.096inch (2.4 mm); thus, having a thickness of 0.013 inch (0.3 mm).

[0228] While the probe assemblies and associated methods of manufacturedisclosed for constructing a suspended, generally coaxial ultrasonictransducer have applications in connection with forming circumferentiallesions to treat atrial fibrillation as described above, those skilledin the art will readily recognize that the present constructions andmethods of manufacture can be used for constructing ultrasonic elementsfor the delivery into and the ablation of other body spaces in thetreatment of other medical conditions, as well as in connection withother applications outside the medical field. For instance, theultrasound ablation device described above and the variations thereofdescribed below may be used for joining adjacent linear lesions in aless-invasive “maze”-type procedure, or be used within the coronarysinus to ablate the atrioventricular (AV) node to treatWolff-Parkinson-White syndrome and any other accessory conductivepathway abnormality. In this latter application, it may be desirably toablate only a portion of the circumference of the coronary sinus. Inaddition, these types of ablation devices can be mounted onto apre-shaped probe shaft that has a curvature that generally matches anatural curvature of the coronary sinus about the exterior of the heart.Such pre-shaped probe may self-orient within the coronary sinus toposition the active ultrasonic transducer toward the inner side of thecoronary sinus (i.e., toward the interior of the heart) so as to directtransmission toward the AV node. A probe constructed with the ultrasonictransducer mounting assemblies disclosed herein can also be designedwithout an anchoring balloon for use on an end of a probe for thetreatment of ventricular tachycardia.

[0229] For various reasons, the “narrow pass filter” device may beparticularly well suited for use in forming circumferential conductionblocks in left atrial wall and pulmonary vein tissues according to thepresent invention. It is believed that the efficiency of ultrasoundtransmission from a piezoelectric transducer is limited by the length ofthe transducer, which limitations are further believed to be a functionof the wavelength of the emitted signal. Thus, for some applications atransducer may be required to be longer than the length which is desiredfor the lesion to be formed. Many procedures intending to formconduction blocks in the left atrium or pulmonary veins, such as, forexample, less-invasive “maze”-type procedures, require only enoughlesion width to create a functional electrical block and to electricallyisolate a tissue region. In addition, limiting the amount of damageformed along an atrial wall, even in a controlled ablation procedure,pervades as a general concern. However, a transducer that is necessaryto form that block, or which may be desirable for other reasons, mayrequire a length which is much longer and may create lesions which aremuch wider than is functionally required for the block. A “narrow pass”filter along the balloon provides one solution to such competinginterests.

[0230] Another variation of the balloon-transducer relationship in anultrasound ablation assembly according to the present invention hasplacement of an ultrasonically absorbent band along balloon and directlyin the central region of the emitted energy signal from transducer.According to this variation, the ultrasonically absorbent band isadapted to heat to a significant temperature rise when sonically coupledto the transducer via the ultrasound signal. It is believed that someablation methods may benefit from combining ultrasound/thermalconduction modes of ablation in a targeted circumferential band oftissue. In another aspect of this variation, ultrasonically absorbentband may operate as an energy sink as an aid to control the extent ofablation to a less traumatic and invasive level than would be reached byallowing the raw ultrasound energy to couple directly to the tissue. Inother words, by heating the absorbent band the signal is diminished to alevel that might have a more controlled depth of tissue ablation.Further to this aspect, absorbent band may therefore also have a widthwhich is more commensurate with the length of the transducer.

[0231] It is further contemplated that, where outer shields, absorbentbands, or sinks are placed over and around the ultrasound transducer,use of the transducer as a position monitoring sensor, as describedherein according to various devices, may be affected. For example, theultrasonic shield or sink may produce a pronounced signal reflecting thedistance of the expanded balloon from the transducer, which signal maymask or otherwise affect the ability to sense the signal that representsthe desired anatomical information radially disposed from the ablationregion along the balloon. Therefore, signal processing or other means torecognize distinctive characteristics of the desired anatomical signalmay be required to decipher between the anatomical ultrasound data andsensed ultrasound data from the shield(s) or sink(s).

[0232] The ultrasonic transducer preferably has an annular shape so asto emit ultrasonic energy around the entire circumference of theballoon. The present circumferential ablation device, however, can emita collimated beam of ultrasonic energy in a specific angular exposure.For instance, the transducer can be configured to have only a singleactive sector (e.g., 180° exposure). The transducer can also have aplanar shape. By rotating the elongate body, the transducer can be sweptthrough 360° in order to form a circumferential ablation. For thispurpose, the transducer may be mounted on a torquible member, in themanner described above.

[0233] Another type of ultrasonic transducer, which can be mounted to atorquible member within the balloon, can be constructed as follows. Thetransducer is formed by curvilinear section and is mounted on thetorquible member with its concave surface facing in a radially outwarddirection. The torquible member desirably is formed with recess thatsubstantially matches a portion of the concave surface of thetransducer. The torquible member also includes longitudinal ridges onthe edges of the recess that support the transducer above the probeshaft such that an air gap is formed between the transducer and thetorquible member. In this manner, the transducer is “air-backed.” Thisspaced is sealed and closed in the manner described above.

[0234] The inverted transducer section produces a highly directionalbeam pattern. By sweeping the transducer through 360° of rotation, asdescribed above, a circumferential lesion can be formed while using lesspower than would be required with a planar or tubular transducer. Thisrotation is achieved by rotating the torquible member, which rotateswithin a lumen of the probe shaft.

[0235] It is to be further understood that the various modes of theultrasound-balloon devices just described may be used according toseveral different particular methods such as those methods otherwise setforth throughout this disclosure. For example, any of the ultrasoundtransducer devices may be used to form a conduction block in order toprevent or treat focal arrhythmia arising from a specific pulmonaryvein, or may alternatively or additionally be used for joining adjacentlinear lesions in a less-invasive “maze”-type procedure.

[0236] A circular array of ultrasonic transducers having the innerelectrode may be used as a common electrode and the cylindricalpiezoelectric material as a common element. The single outer electrode,however, is separated by four longitudinal grooves into four electrodesdisposed about the outer surface of the piezoelectric material. The fourelectrodes correspond to the array of four sensors, each electrodecorresponding to one sensor.

[0237] When an AC voltage is impressed between the inner electrode and aselected one of the four electrodes, the piezoelectric material vibratesin the region between the inner electrode and the selected electrode.For example, an AC voltage impressed between the inner electrode and theelectrode will cause the region between the electrode and the electrodeto vibrate. However, the piezoelectric material is a single piece ofmaterial, so a vibration between the inner electrode and the electrodewill also cause some vibration in the regions between the electrodes.The vibration in the regions between the electrodes will generate avoltage. Thus, the sensors produced by the electrodes are not completelyindependent of one another and there will be some coupling between thesensors.

[0238] The coupling between the sensors produced by the electrodes canbe reduced by extending the longitudinal grooves between the electrodesinto the single piece of piezoelectric material to provide a zonedpiezoelectric material. The grooves in the piezoelectric material willtend to physically separate the piezoelectric material into four zones.Each zone will have less mass than the single piece of piezoelectricmaterial, and thus each of the four zones will typically provide afaster right-down time than the single piezoelectric material.

[0239] The coupling between the sensors produced by the electrodes canbe further reduced by extending the longitudinal grooves all the waythrough the piezoelectric material, thereby producing four separatepieces of piezoelectric material.

[0240] The electrodes can be driven separately thereby providing fourseparate transducers. The electrodes can also be driven in unison toprovide a single transducer.

[0241] Various forms of ablation elements may be suitable for use in anoverall ablation assembly as contemplated within the present invention.

[0242] In one example, the band includes one or more conductiveelectrodes. In one device, the band includes a porous skin that isadapted to allow fluid, such as hypertonic saline solution, to pass froman internal chamber defined by the probe and outwardly to contact thetissues of the ostium. Such a porous skin can be constructed accordingto several different methods, such as by forming holes in an otherwisecontiguous polymeric material, including mechanically drilling or usinglaser energy, or the porous skin may simply be an inherently porousconstruction, such as a porous fluoropolymer, e.g.polytetrafluoroethylene (PTFE), cellulose, polyurethane, or other porousmaterial, blend, or construction. In any case, by electrically couplingthe fluid within the porous balloon skin to an RF current source(preferably monopolar), the porous band serves as an electrode whereinRF current flows outwardly through the pores via the conductive fluid.In addition, it is further contemplated that a porous outer skin may beprovided externally of another, separate expandable member, such as aseparate expandable balloon, wherein the conductive fluid is containedin a region between the porous outer skin and the expandable membercontained therein. Various other “fluid electrode” designs than thosespecifically herein described may also be suitable according to one ofordinary skill upon review of this disclosure.

[0243] In the alternative, or in addition to the RF electrode variationsjust described, the circumferential ablation element may also includeother ablative energy sources or sinks, and particularly may include athermal conductor that circumscribes the outer circumference of theworking length of an expandable member. Examples of suitable thermalconductor arrangements include a metallic element, which can, forexample, be constructed as previously described for the more detailed RFdevices above. In one device, the thermal conductor, such a metallicelement, can be generally either resistively heated in a closed loopcircuit internal to the probe, or conductively heated by a heat sourcecoupled to the thermal conductor. In the latter case of conductiveheating of the thermal conductor with a heat source, the expandablemember may be for example a polymeric balloon skin which is inflatedwith a fluid that is heated either by a resistive coil or by bipolar RFcurrent. In any case, it is believed that a thermal conductor on theouter surface of the expandable member is suitable when it is adapted toheat tissue adjacent thereto to a temperature between 40° and 80° C.

[0244] As noted above, the probe assembly can include one or moretemperature sensors (e.g., thermocouples) to (1) determine the positionof the ablation member and/or (2) monitor tissue ablation. Thus, suchtemperature sensors can be used in conjunction with all of the positionmonitoring systems described above.

[0245] The probe assembly can also include one or more electrodesarranged to make contact with venous and/or cardiac tissue adjacent thetargeted region of tissue. Such electrodes desirably are arranged forelectrical mapping purposes as well as to check the integrity of theconductive block after ablation of the region of tissue. For instance,in one mode, an electrode is mounted distal of the ablation element andis used to invoke an arrythemogenic condition in venous/cardiac tissuedistal of the formed lesion. This electrode can be used by itself or incombination with one or more electrodes that are positioned proximallyof this distal-most electrode.

[0246] One or more of these proximal electrodes can be used to map theresponsive electro-physicological response to determine whether theresponse transcends the formed lesion (i.e., the produced conductiveblock). In one variation, the probe includes only one distal electrodeand a proximal electrode positioned on opposite sides of the ablationelement. In another variation, the probe includes an array of electrodespositioned along a length of the probe. When the expandable member liesin a collapsed position, the distal portion of the delivery member canbe manipulated to position the array of electrodes against the tissueand across the formed lesion. In this manner, the integrity of theformed conduction block being formed can be monitored and checked.

[0247] Both temperature sensors and electrodes desirably are arrangedalong at least a portion of the length of the expandable member (e.g.,the inflatable balloon). The following provides a description of severalways to attach such sensors and electrodes to or use such sensors andelectrodes with an expandable member.

[0248] The temperature sensor devices herein described are believed tobe particularly well suited for use with highly elastomeric balloons,wherein such designs are at least in part intended to account for andaccommodate high amounts of elongation at the balloon/sensor interface.More particular examples of such highly compliant or elastomericballoons are described elsewhere in this disclosure.

[0249] Notwithstanding the highly beneficial aspects of such assemblies,the embodiments may also be combined with other non-compliant balloonvarieties, or may be further coupled to other ablation members notincorporating balloons, such as for example those using expandablecages, wherein the outer perimeter of such cage may be interchangeablysubstituted with the balloon skin in the devices described. In othermore isolated instances, the temperature monitoring sensor assembliesherein disclosed may be combined with certain circumferential ablationmembers without reliance on any particular circumferential ablationmember design, such as in the event of deployable thermocouple splinesthat may be positioned in a circumferential pattern in order to monitorablation in a manner that is relatively independent of the ablationmember features.

[0250] Suitable shapes for the thermocouple include, but are not limitedto, a loop, an oval loop, a “T” configuration, an “S” configuration, ahook configuration or a spherical ball configuration. Such shapes aredesirable both for anchoring the thermocouple to the balloon and forsensing the temperature of tissue outside the balloon. That is, in eachof the above shapes a portion of the thermocouple lies generally normalto, or at least skewed relative to, the axis of the thermocouple wire toenhance the coupling between the thermocouple and the adhesive thatbonds it to the balloon wall, as described below. These shapes alsoprovide more surface area for the thermocouple without lengthening thethermocouple. These thermocouples, with more exposed area than astraight thermocouple, are believed to have better accuracy and responsetime.

[0251] The thermocouple is attached to an inside wall of the balloon bya fastener. In one variation, the fastener is a bead of adhesive that iscompatible with the material used for manufacturing the balloon.Suitable adhesives include, but are not limited to, epoxies,cyanoacetate adhesives, silicone adhesives, flexible adhesives, etc. Inalternate embodiments, the fastener is a tape that is bonded to theballoon, a bead of material that is molded or heat-bonded to theballoon.

[0252] The thermocouple wire preferably has sufficient flexibility sothat it does not seriously impede the expansion of the balloon.Additionally, according to one highly beneficial aspect of theembodiment, the thermocouple wire is provided with a looped orsingle-turn spring shape so that the wire expands with the balloon, andagain does not seriously impede the expansion of the balloon, as well asnot pull on the embedded thermocouple when the balloon is expanded.

[0253] Thermocouple wires may be cut to the desired length and thensoldered where the temperature monitoring is to be made—such solderremoves insulation between the individual strands of the bifilar andelectrically couples the leads in a manner that is sensitive to changesin temperature. Notwithstanding the benefits provided by suchthermocouples in the present embodiments, other well-known temperaturesensors may be suitable substitutes for the thermocouples describedherein without departing from the scope of the invention.

[0254] The attachment points are typically located in high-stress areas.In one embodiment, the wall of the balloon may be reinforced nearattachment points. More specifically, a reinforcement wherein the wallsurface of the balloon is thickened on an inner side near the attachmentpoint. Thickening the inner surface wall provides increased strengthwhile still maintaining a smooth outer surface of the balloon, thusallowing the balloon to be easily manipulated inside the body of thepatient.

[0255] Where a thermocouple is positioned within the path of ablativecoupling between an ablation element within the balloon and theballoon/tissue interface, there may be false temperature readings forthat thermocouple due to a response of the thermocouple itself to theablation energy (e.g. ultrasonic heating of the thermocouple within anultrasonic ablation energy path may heat the thermocouple to a greatertemperature than its surroundings). In this case, providing multiplethermocouples at different locations and comparing their operatingparameters (e.g. response times, etc.) may provide useful information toallow certain such variables to be filtered and thereby calculate anaccurate temperature at the thermocouple location.

[0256] An ablation system can be provided with electrodes to be used formapping the conductivity of the pulmonary vein and to ascertain theeffectiveness of the ablation. A distal electrode is distal to anablated region of the tissue and the proximal electrode is proximal tothe ablated region. According to this orientation, the distal andproximal electrodes are positioned to allow the monitoring of an actionpotential across the ablation zone where the thermocouple is located,thereby enabling a user to confirm formation of a conduction blockeither during or after performing an ablation procedure with theassembly.

[0257] Referring again to FIG. 19, the ablation probe 100 also desirablyincludes feedback control. For instance, the expandable member 106 caninclude one or more thermal sensors 146 (e.g., thermocouples,thermistors, etc.) that are provided to either the outer side or theinside of the expandable member 106. Monitoring temperature at thislocation provides indicia for the progression of the lesion. If thetemperature sensors are located inside the expandable member 106, thefeedback control may also need to account for any temperature gradientthat occurs through the wall of the expandable member. If the sensorsare placed on the exterior of the expandable member, they may also beused to record electrogram signals by reconnecting the signal leads todifferent input port of a signal-processing unit. Such signals can beuseful in mapping the target tissue both before and after ablation.

[0258] The thermocouples and/or electrodes desirably are blended intothe expandable member in order to present a smooth profile. Transitionregions, which are formed by either adhesive or melted polymer tubing,“smooth out” the surface of the expandable member as the surface stepsup from the outer surface of the expandable member to the thermocouplesurface. Various constructions to integrate the thermocouples and/orelectrodes into the expandable member, as well as various approaches tousing thermocouples and electrodes with an expandable member, aredescribed in detail below.

[0259] The ablation probe assembly of the present invention is designedfor treatment of the more common forms of atrial fibrillation, resultingfrom perpetually wandering reentrant wavelets. Such arrhythmias aregenerally not amenable to localized ablation techniques, because theexcitation waves may circumnavigate a focal lesion. Thus, the probeassembly uses the ablation element to form a substantiallycircumferential lesion, or lesions, to segment the atrial tissue so asto block conduction of the reentrant wave fronts.

[0260] Delivery of energy (e.g., thermal, RF, ultrasonic, electrical,etc.) to the tissue of the pulmonary vein ostium is commenced once theablation element is positioned at the desired location and anchoredthere by expansion of the expandable member. Good coupling of the energyproduced by the ablation element with the tissue facilitates creation ofa continuous lesion. Energy from the ablation control system istypically delivered to the ablation element via electrical conductorleads. The ablation control system includes a current source forsupplying current to the ablation element, a monitoring circuit, and acontrol circuit. The current source is coupled to the ablation elementvia a lead set (and to a ground patch in some modes). The monitorcircuit desirably communicates with one or more sensors (e.g.,temperature and/or current sensors) which monitor the operation of theablation element. The control circuit is connected to the monitoringcircuit and to the current source in order to adjust the output level ofthe current driving the ablation element based upon the sensed condition(e.g., upon the relationship between the monitored temperature and apredetermined temperature set point).

[0261] In some modes of the present deflectable ablation probe, aposition monitoring system may be employed to facilitate positioning ofthe ablation member. The position monitoring system includes a sensorcontrol system and a display. The sensor control system communicateswith one or more sensor elements located in, or near the expandablemember. In one variation, the ablation element and sensor element arecombined in a single element that provides both sensing and ablationcapabilities. In other variations, separate elements are used for theablation element and the sensor element(s).

[0262] An ultrasonic position monitoring system uses a single,circumferentially symmetric ultrasonic transducer. The sensor can be theultrasonic ablation element, or a separate ultrasonic transducer inaddition to an ultrasonic ablation element. The transducer is positionedin a pulmonary vein, and the transducer is operably connected to asensor control system. In one device, the sensor control system is aPanametrics Model 5073PR. The sensor control system includes atransmitter, a receiver, and a diplexer. An output from the transmitteris provided to a transmitter port (port 1) of the diplexer. An outputfrom a receiver port (port 3) of the diplexer is provided to an input ofthe receiver. A transducer port (port 2) of the diplexer is providedthrough a connector to the transducer. An output from the receiver isprovided to the display.

[0263] A diplexer is commonly used in radar and sonar systems to isolatethe transmitter output from the receiver input. Energy provided to thetransmitter port of the diplexer (port 1) is provided to the transducerport (port 2) of the diplexer, but not to the receiver port of thediplexer (port 3). Energy provided from the transducer to the transducerport of the diplexer (port 2) is provided to the receiver port (port 3)of the diplexer, but not to the transmitter port (port 3) of thediplexer.

[0264] The diplexer can be a circulator or an electronically controlledswitch controlled by a timing generator. The timing generator sets theswitch to connect the transmitter to the transducer for a first timeperiod. The timing generator then sets the switch to connect thereceiver to the transducer for a second time period. By switching thetransducer between the transmitter and the receiver, the diplexereffectively “timeshares” the transducer between the transmitter and thereceiver.

[0265] The transmitter generates a signal that drives the transducer.When the diplexer connects the transmitter to the transducer, the drivesignal from the transmitter causes the transducer to emit an ultrasonicsound wave. The ultrasonic sound wave propagates through the interior ofthe expandable member, through the wall of the expandable member, andreflects off of the inner wall of the ostium. The reflected ultrasonicenergy returns to the transducer and causes the transducer to generatean echo signal. The echo signal is provided through the diplexer to thereceiver. The receiver amplifies and processes the echo signal toproduce a display signal. The display signal is provided to the display.

[0266] The transducer transmits a radiated wave. For a cylindricallysymmetric transducer, the radiated wave will approximate a cylindricalwave that expands away from the transducer. When the cylindrical wavereaches the ostium, the wave will be reflected in a substantiallycylindrically symmetric fashion to produce a reflected wave that issimilar to a cylindrical wave as well. The reflected wave propagatesback to the transducer.

[0267] Reflections will occur when the ultrasonic sound wave propagatingin a medium strikes a transition (or interface) in the acousticproperties of the medium. Any interface between materials havingdifferent acoustic properties will cause a portion of the wave to bereflected.

[0268] The transmitted pulse causes the transducer to vibrate (in amanner very similar to a bell) during the ring-down period therebyproducing the ring-down signal. The echo pulse is caused by ultrasonicenergy that is reflected from the ostium back to the transducer. Duringthe ring-down period it is difficult to see signals caused byreflections (such as the signal) because the signals produced byreflections are typically relatively small in amplitude and are easilymasked by the relatively large amplitude portions of the ring-downsignal. Thus, it is difficult to detect reflections from targets thatare so close to the transducer that their reflections return during thering-down period. This can limit the minimum useful range of thetransducer.

[0269] The ring-down time of the transducer can be reduced byconfiguring the transmitter to provide a shaped transmit pulse. Theshaped transmit pulse drives the transducer in a manner that reduces theamplitude of the ringing and shortens the ring-down period. Since thering-down period is shorter, the shaped transmit pulse allows thetransducer to be used to detect targets at a shorter distance.

[0270] In a device where the transducer is also used as the ablationelement, the transmitter provides two power modes, a low-power mode usedfor position measurements, and a high-power mode used for ablation. Whenablation is desired, the diplexer stops switching between the receiverand the transmitter, and stays locked on the transmitter while thetransmitter operates in the high-power mode.

[0271] Ultrasonic ablation requires that the transducer produce anultrasonic wave having relatively higher power. Higher power typicallyrequires a transducer having a relatively large physical size. Largertransducers often have longer ring-down times. While the use of a shapedtransmitter pulse will reduce ring-down times, for some transducers eventhe use of a shaped transmit pulse does not shorten the ring-down timesufficiently to allow the ablation element to be used for positionsensing. Moreover, in some devices, the ablation element is not anultrasonic transducer, and thus may be unsuitable for use as a positionsensor. Thus, in some devices, it is desirable to add one or moreultrasonic transducers to be used for position sensing.

[0272] One more detailed construction for a cylindrical ultrasoundtransducer for use in the present application is as follows. The lengthof the transducer or transducer assembly (e.g., multi-element array oftransducer elements) desirably is selected for a given clinicalapplication. In connection with forming circumferential condition blocksin cardiac or pulmonary vein wall tissue, the transducer length can fallwithin the range of approximately 2 mm up to greater than 10 mm, andpreferably equals about 5 mm to 10 mm. A transducer accordingly sized isbelieved to form a lesion of a width sufficient to ensure the integrityof the formed conductive block without undue tissue ablation. For otherapplications, however, the length can be significantly longer.

[0273] Likewise, the transducer outer diameter desirably is selected toaccount for delivery through a particular access path (e.g.,percutaneously and transeptally), for proper placement and locationwithin a particular body space, and for achieving a desired ablationeffect. The positioning of the transducer within an inflatable member,e.g., a balloon, may be desirable for facilitating the positioning ofthe transducer within a pulmonary vein or pulmonary vein ostium at asuitable distance for delivering a circumferential lesion. Thetransducer preferably has an outer diameter within the range of about1.8 mm to greater than 2.5 mm. It has been observed that a transducerwith an outer diameter of about 2 mm generates acoustic power levelsapproaching 20 Watts per centimeter radiator or greater withinmyocardial or vascular tissue, which is believed to be sufficient forablation of tissue engaged by an outer balloon for up to about 2 cmouter diameter of the balloon. For applications in other body spaces,the transducer applicator may have an outer diameter within the range ofabout lmm to greater than 3-4 mm (e.g., as large as 1 to 2 cm forapplications in some body spaces).

[0274] For this purpose, the transducer seats coaxial about the innermember and is supported about the inner member in a manner providing agap between the inner member and the transducer inner tubular member.That is, the inner tubular member forms an interior bore that looselyreceives the inner member. Any of a variety of structures can be used tosupport the transducer about the inner member. For instance, spacers orsplines can be used to coaxially position the transducer about the innermember while leaving a generally annular space between these components.In the alternative, other conventional and known approaches to supportthe transducer can also be used. For instance, O-rings that circumscribethe inner member and lie between the inner member and the transducer cansupport the transducer. More detailed examples of the alternativetransducer support structures just described are disclosed in U.S. Pat.No. 5,620,479 to Diederich, issued Apr. 15, 1997, and entitled “Methodand Apparatus for Thermal Therapy of Tumors,” and U.S. Pat. No.5,606,974 to Castellano, issued Mar. 4, 1997, and entitled “CatheterHaving Ultrasonic Device.”

[0275] In one embodiment, suspending the transducer from an externalprotective layer resolves problems associated with maintaining aminimally damped internal mounting scheme. With reference to FIGS. 32Aand 32B, the external layer coupled to the transducer with a couplingadhesive is described below.

[0276] The transducer 904 is generally coaxially disposed over thetracking member 900; however, it is understood that the transducer 904can be asymmetrically positioned relative to an axis of the guide membertracking member 900 provided an air gap exists between the transducerinner surface and the tracking member 900. An air space 906 existsbetween the transducer 904 and the tracking member 900, therebyproviding an air-backing to maximize the outward radiation of theultrasonic energy, as described above.

[0277] The transducer 904 is held suspended over the tracking member 900by the cooperative arrangement of an outer cover 910, for example, ashrink-wrap polymeric material (e.g., PET), and end plugs 912 bonded toa length of the tracking member 900 proximal and distal to thetransducer 904. In the embodiment illustrated in FIGS. 32A and B, theend plugs 912 are formed of adhesive and lie under the cover 910, and alayer of adhesive 908 covers the transducer 904 and couples thetransducer 904 to an inner surface of the outer cover 910.

[0278] The proper air gap may be ensured during setting of the adhesiveend plugs 912 by inserting three or more beading mandrels between thetracking member and the transducer. These mandrels would preferably beevenly distributed radially about the tracking member 900 and would runaxially along the length of the transducer 910. The beading mandrels canbe sized so as to create a desired air gap (e.g., 0.005 inches (0.13mm)). Since the mandrels must be removed, it is preferred that thebeading mandrels be made out of a material to which the epoxy adhesivewill not stick, such as for example, metal or silicone, and extendbeyond one end of the transducer 904 during the assembly process.

[0279]FIG. 32B is a cross-sectional view through the transducer alongline B—B of FIG. 32A. The thickness of the adhesive layer can be in therange of about 0.0005 (0.013 mm) to about 0.001 inches (0.025 mm). Thecover can have a thickness in the range of about 0.001 to about 0.003inches.

[0280] In addition, the present embodiment may also include an externalcover layer surrounding the ablation member. The material may be athermoset elastomer, such as urethane or silicon rubber. Altematively,the material could be a thermoplastic polymer, such as polyurethane,PET, or any other polymeric thermoplastic. The material could also be anadhesive.

[0281] In an alternative embodiment, the transducer may be suspended bymounting flanges which extend from either end of the transducer. Themounting flanges may be formed in a variety of configurations. An endcap made of suitable plastic or elastomer may also receive the mountingflange.

[0282] The embodiments described herein are particularly useful inassemblies adapted for ablating a circumferential region of tissue wherea pulmonary vein extends from a left atrium in the treatment of atrialfibrillation, as noted above. The circumferential pulmonary veinablation aspect of the invention is therefore suited for combination oraggregation with, or where appropriate in substitution for, the variousfeatures and embodiments disclosed in the following patents andco-pending U.S. Pat. Applications that also address circumferentialablation at a location where a pulmonary vein extends from an atrium:U.S. Ser. No. 08/889,798 for “Circumferential Ablation Device Assembly”to Lesh et al., filed Jul. 8, 1997, now U.S. Pat. No. 6,024,740, issuedon Feb. 15, 2000; U.S. Ser. 08/889,835 for “Device and Method forForming a Circumferential Conduction Block in a Pulmonary Vein” to Lesh,filed Jul. 8, 1997, now U.S. Pat. No. 6,012,457, issued Jan. 11, 2000;U.S. Ser. No. 09/199,736 for “Circumferential Ablation Device Assembly”to Diederich et al., filed Feb. 3, 1998, now U.S. Pat. No. 6,117,101,issued Sep. 12, 2000; and U.S. Ser. 09/260,316 for “Tissue AblationDevice Assembly and Method of Forming a Conduction Block Along a Lengthof Tissue” to Langberg et al., filed Mar. 1, 1999. The disclosures ofthese references are herein incorporated in their entirety by referencethereto.

[0283] It is further contemplated that the embodiments and variationsthereof shown and described herein may be combined, assembled together,or where appropriate substituted for, the various features andembodiments which are disclosed in the following patents and U.S. patentapplications Ser. No. 09/517,614, filed on Mar. 2, 2000 for “MEDICALDEVICE WITH SENSOR COOPERATING WITH EXPANDABLE MEMBER”; U.S. Ser. No.09/435,283, filed on Nov. 5, 1999 for “CIRCUMFERENTIAL ABLATION DEVICEASSEMBLY AND METHODS OF USE AND MANUFACTURE PROVIDING AN ABLATIVECIRCUMFERENTIAL BAND ALONG AN EXPANDABLE MEMBER”; U.S. Ser. No.09/569,735 for “BALLOON ANCHOR WIRE”, filed May 11, 2000; U.S. Ser. No.09/435,281, filed on Nov. 5, 1999 for “TISSUE ABLATION DEVICE ASSEMBLYAND METHOD FOR ELECTRICALLY ISOLATING A PULMONARY VEIN OSTIUM FROM APOSTERIOR LEFT ATRIAL WALL”, U.S. Ser. No. 09/435,280, filed on Nov. 5,1999 for “APPARATUS AND METHOD INCORPORATING AN ULTRASOUND TRANSDUCERONTO A DELIVERY MEMBER”; and U.S. Ser. No. 09/517,472, filed on Mar. 2,2000 for “POSITIONING SYSTEM AND METHOD OF ORIENTING AN ABLATION ELEMENTWITHIN A PULMONARY VEIN.” The disclosures of these references are hereinincorporated in their entirety by reference thereto.

[0284] In addition, such a circumferential ablation device assembly maybe used in combination with other linear ablation assemblies andmethods, as noted above, and various related components or steps of suchassemblies or methods, respectively, in order to form a circumferentialconduction block adjunctively to the formation of long linear lesions,such as in a less-invasive “maze”-type procedure. Examples of suchassemblies and methods related to linear lesion formation and which arecontemplated in combination with the presently disclosed embodiments areshown and described in the following additional patents and U.S. PatentApplications: U.S. Pat. No. 5,971,983, issued on Oct. 26, 1999, entitled“TISSUE ABLATION DEVICE AND METHOD OF USE” filed by Lesh on May 9, 1997;U.S. Ser. No. 09/260,316 for “TISSUE ABLATION SYSTEM AND METHOD FORFORMING A CONDUCTION BLOCK ALONG A LENGTH OF TISSUE” to Langberg et al.,filed May 1, 1999; and U.S. Ser. No. 09/073,907 for “IRRIGATED ABLATIONDEVICE ASSEMBLY”, to Schaer et al., filed May 6, 1998. The disclosuresof these references are also herein incorporated in their entirety byreference thereto.

[0285] While a number of variations of the invention have been shown anddescribed in detail, other modifications and methods of use contemplatedwithin the scope of this invention will be readily apparent to those ofskill in the art based upon this disclosure. It is contemplated thatvarious combinations or sub-combinations of the specific embodiments maybe made and still fall within the scope of the invention. Moreover, allassemblies described are believed useful when modified to treat othertissues in the body, in particular other regions of the heart, such asthe coronary sinus and surrounding areas. Further, the disclosedassemblies may be useful in treating other conditions, wherein aberrantelectrical conduction may be implicated, such as for example, heartflutter. Indeed, other conditions wherein probe-based, directed tissueablation may be indicated, such as for example, in the ablation offallopian tube cysts. Accordingly, it should be understood that variousapplications, modifications and substitutions may be made of equivalentswithout departing from the spirit of the invention.

What is claimed is:
 1. A method for treating atrial arrhythmia in apatient by forming a conduction block along a circumferential region oftissue at a location where a pulmonary vein extends from an atrium,comprising: providing a surgical ablation probe having a handle and ashaft with a proximal end portion and a distal end portion, wherein saidshaft further comprises an anchoring mechanism and an circumferentialablation member located along said distal end portion of said shaft;inserting said shaft through an opening in a patient's chest; advancingsaid surgical ablation probe into said atrium; anchoring saidcircumferential ablation member at said location; and supplying energyto said circumferential ablation member, such that said circumferentialablation member ablatively couples to at least a portion of saidcircumferential region of tissue, thereby forming said conduction block.2. The method of claim 1, further comprising monitoring an electricalactivity of said atrium before supplying energy to said circumferentialablation member, in order to identify said location.
 3. The method ofclaim 1, further comprising monitoring an electrical activity of saidatrium after supplying energy to said circumferential ablation member,in order to evaluate said efficacy of said conduction block in treatingsaid arrhythmia.
 4. The method of claim 1, wherein said surgicalablation probe is advanced into said atrium via trans-thoracic surgery.5. The method of claim 1, wherein said surgical ablation probe isadvanced into said atrium through an atriotomy in a left atrialappendage.
 6. The method of claim 1 wherein said surgical ablation probeis advanced into said atrium via a minimally invasive access technique.7. The method of claim 6 wherein said access technique comprises a chestaccess device.
 8. The method of claim 7 wherein said chest access devicecomprises a trocar.